INTRODUCTION
Geografically, the district of Bages belongs to the Central Catalonian depression which is the eastern sector of the basin of the river Ebre. This low lands region borders on the mountain range of Pyrenees by the north, on the Catalonian Coastal range by the east and on the Iberian range by the south-west. During part of the tertiary period, this basin or depression was filled up by sediments that came from the relieves around it. Therefore, sedimentary stones from that period like conglomerates, sandstones, mudstones, limestones and eventually evaporites are found in this area. Most of the actual stones in the district of Bages were laid in the superior Eocene period or in the beginning of Oligocene. Nevertheless, modern detrital sediments are found as well mainly near the rivers. These quaternary sediments constitute gravel deposits.
As a rule, the layers of rocks in this area do not show intense deformations. In most of the area, the layers only slant softly toward the north-east, but strongly folded layers are found in the north of the region.
 |
 |
|
The horns or needles [Les Agulles] in Montserrat |
Tabular relief in the valley of Rajadell |
The main shapes of this land are due to the differential erosion, thus, to the specific resistance to the erosion of every kind of rock. The district of Bages includes the following three basic types of land morphologies: Montserrat type, tabular and folded areas.
MONTSERRAT TYPE
The particular shapes of Montserrat massif set the so-called Montserrat relief type. Undoubtedly, the slim monoliths or needles are its most spectacular and characteristic morphology. The current relief of Montserrat comes from the interaction of three elements: the rock material, the structure and the erosion.
The material is the conglomerate, a rock made of a different nature stones that are glued in a matrix of sand, clay and calcareous concrete. As a whole, conglomerate rocks are very homogeneous and resistant to the erosion.
The structure is a deep deposit of almost flat layers of conglomerate rock with a net of vertical fractures that isolates columns.
The erosion by water and ice which is reponsible for sculpting and rounding the columnar structures.
Thin layers of easy to erode clay alternate with the conglomerate rock The vegetation grows on these clay layers. Often they are related to the presence of caves.
In the near area of Sant Llorenç del Munt i Serra de l'Obac natural park, fractures are more distant than in Monserrat. That's why the erosive model produces there rounder summits like, for instance, Montcau.
TABULAR
The tabular morphology of slopes that culminate in almost flat surfaces like a table comes from the erosion in non-folded areas. The tabular morphology is originated by the alternation of soft rock layers in the slopes (with mudstones predominance) and hard layers in the summits (with conglomerates, sandstones, and limestones eventually). The best tabular morphologies cases are located in the south-west area of Bages (Cogulló de Cal Torre, Pòpia de Montgròs, Collbaix,...).
FOLDED AREAS
The tectonic forces of Pyrenees which were pressing from the north together with the plastic behaviour of the salt of the geological formation Cardona beneath folded the rock layers in the north of Bages district. Violent anticline structures follow the direction SW-NE in parallel to the Pyrenees. The most abrupt anticlines are cut in faults often with long displacements. The oldest rocks, like salt in Cardona and gypsum in Súria and Santa Maria d'Oló, appear in the eroded open centers of these anticlines. From the NW corner of the district to the SE, the sequence of large anticline structures is as follows:
- Anticline of Pinós and dome of Cardona
- Anticline north of Súria
- Fault of Mig-Món (Súria) and anticline of Balsareny
- Antciline of Súria and fault of El Tordell (Súria)
- Anticline of de Santa Maria d'Oló
- Detachment of El Guix (Sallent)
Rocks are natural, inorganic and solid compounds made up of one or more minerals. In some cases, they also can contain pieces of former rocks or remains of living organisms. The rocks in Bages area are conglomerates, sandstones, mudstones, limestones, evaporites and the different stones in gravel deposits. Unless evaporites, all these rocks contain calcium carbonate; thus the resulting soils also contain calcium carbonate.
 |
CONGLOMERATES
Conglomerates are detrital rocks that are made up basically of round, bigger than 2 cm diameter pieces which are called pebbles. The pebbles are included in a matrix made of sand, silt and clay. All these components are stuck by the cement, which here is always the calcium carbonate. The biggest mass of conglomerates is located in the south and in the south-east of the district of Bages. Conglomerates are also frequent in the rest of the territory, mainly on top of the tabular relieves or within layers of thinner particles rocks.
 |
GRAVELS
Gravels are detrital, non-cemented sediments made up of over 2 cm diameter stones. Although with exceptions, in the area of Bages these fragments are usually round as a result of its transport by rivers. They are usually included in a sandy and clayey matrix. They were laid during quaternary period, therefore they're the newest geological materials of the region. The gravels are common in the riverbeds and in the fluvial terraces. The fluvial terraces witnesses the level of the rivers some hundreds of thousands of years ago. Some deposits of gravels have been exploited.
 |
SANDSTONES
Sandstones are detrital rocks that result from the cementation of sands which, in their turn, are generally included in a matrix of smaller size particles. The sands are fragments of minerals or rocks with diameters between 2 and 1/16 mm. The cement of the sandstones in the district of Bages is calcium carbonate.
Sandstones of both continental and marine sources are common all around the region. Often, iron oxides dye in red, rusty color the sandstones of continental origin. Sandstones are found whether in thin layers into other rocks (mainly mudstones) or in big, homogeneous packs that usually have been or are currently being exploited. Sandstones were used in most of the ancient buildings of the area because their availability and ease to shape.
 |
 |
MUDSTONES
Mudstones are detrital rocks made up of less than 1/16 mm diameter particles. If these fragments are coherent, then the rock is named siltstone in case of the particles are above 1/256 mm size or claystone in case of below 1/256 mm. If these fragments do not have enough coherence, then the rock is called silt and clay. The mudstones that contain 50% of calcium carbonate on average (35%-65% according to Vatan) are called loams. They're usually bluish color. The color of mudstones in the area of Bages changes from the bluish gray or yellowish of the sediments of marine origin, to the characteristic reddish of those sediment of continental origin which contain iron oxides.
The extraordinary hollow out of the morphology of Bages is a consequence of the scarce resistance in front of the erosion of the mudstones. Mudstone materials predominate in the farmed plains. Mudstones are used in the manufacture of ceramics and bricks for building purposes.
 |
LIMESTONES
Limestones are calcareous rocks made of, basically, calcium carbonate. The most frequent limestones in Bages are arranged in really resistant to the erosion layers. They come from whether marine or lake origin. Nowadays limestones are mined in quarries as a material for construction while, formerly, they were used to obtain lime. Marine limestones of Bages contain a lot of microfossils because their were originated in past coral reefs.
Travertines, which are also found in the area, are light and porous calcareous rocks made up of calcium carbonate that laid on plants, next to water springs.
 |
EVAPORITES
Halite, potassic salts (silvita and carnalite) and gypsum are evaporites. These are soluble rocks that come from the precipitation of the salt from an ancient sea, subsequent to the water evaporation. In Bages area, gypsum comes to the surface just in a handful of locations. The most outstanding emergence of evaporites is the mountain of salt of Cardona (Muntanya de sal de Cardona) where salt has been extracted from long ago. The main structure of the mountain of salt of Cardona is a diapir which is located in the middle of a folding. The salt pushed through the layers on top after its plastic behavior and its low density in comparison to the materials surrounding and covering it.
When the salt mountain is looked closer, the thin layers of salt and clay show a tangled picture while its surface looks like a rake of sharp edges and minute channels as a consequence of the solution of the salt in raining water. The colourful combination of thin and twisted layers of different materials astonishes the visitor of the mountain of salt of Cardona. Halite, the most abundant mineral, is colorless or white, orange or pink according to its content of different impurities, while mudstone is gray.
THE MINERALS
Minerals are homogeneous, inorganic solids of natural origin with a specific chemical composition (however often this composition is not totally fixed) and an arranged atomic structure (crystalline structure). Most of the minerals are produced by inorganic processes, but minerals like aragonite from the shells of mollusks are made by living organisms. Crystal means any solid with crystalline structure, but often the name is applied just to the minerals with a polyhedral shape dispaying the internal atomic order. Minerals with a perfect polyhedral shape are very rare in nature because they require specific conditions of origin. Minerals, usually in small or microscopic crystal shape, are the main components of the rocks. Anyway, different processes of mineralization may concentrate some minerals until growing relevant size crystals.
All rocks in the area of Bages were originated by sedimentation. Therefore, the minerals of the area are not particularly diverse. On the other hand, minerals that are made up of sulfates and carbonates are quite common and minerals of chlorides from the Cardona geological formation are really outstanding.
 |
CALCITE (CaCO3, calcium carbonate)
Calcite is a mineral that crystallizes in several shapes, producing crystals generally white or colorless, although sometimes they can be different colors. Calcite defines the third degree of hardness of Moh's scale. It cannot be scraped by the nail, but it is easily scraped by a knife. Calcite crystals are often found coating the cracks of CaCO3 containing stones and in caves. Calcite is the main component of limestones that are used in the manufacture of cement and lime.
 |
MALACHITE (Cu2(OH)2CO3,
copper basic carbonate)
Malachite eventually appears as a prismatic acicular crystals of the monolithic system or, often, as patinas, powdery coatings or reniform or globular masses. It has a beautiful, characteristic green color, green streak and 3,5 - 4 hardness degree. Malachite is a source of copper and, after its beauty, it is used in jewels.
In the district of Bages, malachite is located mainly in Artés, in the so-called red-bed copper mineralization. The mineralization process consists first in the washing (lixiviation) of copper ions with water and then their precipitation as sulfides when suddenly a reductor level was reached. Finally, the carbonatation of the sulfides turns the copper mineral to malachite and azurite. The process of malachite formation is the real interesting thing in Artés, rather than the size of the crystals or the amount of the deposit. Malachite can be found in Cabrianes (Sallent), Santpedor and Ferrerons (Moià) as well.
 |
AZURITE (Cu3(OH)2(CO3)2, copper basic carbonate)
Azurite produces different kinds of crystals of the monolithic system, but it is commonly found as patinas or reniform or powdery masses. Usually, azurite and malachite are found together, but azurite can turn into malachite by chemical alteration. Azurite has a beautiful Indian blue color, blue streak and 3,5-4 hardness degree. Azurite is a secondary source of copper and it is used as an ornamental stone too.
Although less abundant than malachite, azurite is found in Sallent and Artés, in the so-called red-bed copper mineralization (see malachite) that are located at the bottom of paleochannels (ancient riverbeds) in Artés geological formation.
 |
PYRITE (FeS2,
iron disulfide)
Pyrite crystallizes in the regular system, in cubes and pentagonal dodecahedrons of yellow brass color. The hardness of pyrite is 6 -it cannot be grated with a knife but with a quartz crystal-. In Bages, pyrite is found in gray mudstones stratums of marine origin. The crystal size usually is less than 4 millimeters. Often, pyrite builds aggregates that refill ancient galleries that were opened by marines invertebrates -the so-called burrows-. One of the world most important deposit of pyrite is located in Río Tinto (Huelva). Pyrite is exploited mainly to manufacture sulfuric acid and also as a source of iron.
 |
HEXAHIDRITE (MgSO4·6H2O,
hydrous magnesium sulfate)
Hexahidrite is a fibrous mineral that coats with white, delicate efflorescences the surface of magnesium containing humid rocks. Hexahidrite has the typically bitter taste of magnesium and it is so soft (hardness 2-2,5) that can be grated with a nail. Manresa is a well known location of this mineral which is usually rare. Hexahidrite is quite similar to epsomite (MgSO4·H2O) by the appearance and the chemical composition, they only differ from the water of hydration.
 |
GYPSUM (CaSO4·2H2O,
hydrous calcium sulfate)
Gypsum is a colorless, white, gray or red mineral, but always with an obvious white streak. Gypsum is soft; it defines the hardness degree 2 -the minerals that can be scraped with the nail- in the Moh's scale. Gypsum crystallizes in different shapes: translucent sheets with an excellent exfoliation, colorless crystals with acute arrowhead shape, fibers, compact masses made by tiny, white crystals (variety alabaster). The most frequent gypsum is the so-called secondary gypsum that comes from the hydration of anhydrite (Ca SO 4 ). Once more, anhydrite was originated from a primary gypsum.
Most of the gypsum in Central Catalonia deposited in the period Eocene, during the first stages of evaporation of the sea that covered this region. This process ended up with the deposit of halite and silvine of the geological formation Cardona. There is gypsum in the borders of this formation, for instance Artés, Avinyó, Igualada, Òdena and Castellterçol, and also below the salt deposit. Furthermore, there is gypsum in Súria and Sallent that comes from the evaporation of continental lagoons. Gypsum is currently extracted in Igualada and Òdena, two villages in the district of Anoia close to the south-west of Bages. Gypsum was also mined in Súria and Artés, always for construction. The clayey stratums of the Artés geological formation are often crossed by narrow veins of white, fibrous gypsum.
 |
HALITE (NaCl, sodium chloride)
Halite or common salt has a hardness of 2 -can be grated by the nail- and crystallizes in cubes that can achieve big sizes (even more than a cubic meter!). Pure halite is colorless, but the presence of impurities turns it to different colors. In Bages, halite is often reddish because the presence of iron oxides. Most of the Cardona geological formation -a pack of stratums 300 m thick in the unfolded areas- is made up of halite. This formation spreads in the subsoil in a large area of the Central Catalonia that comprises the north of Bages district. Its unique outcrop is the salt mountain of Cardona, where halite is exploited probably since the prehistory. Halite was also mined in Súria.
 |
SILVITE or SILVINE (KCl,
potassium chloride)
Silvite, like halite, crystallizes in cubic system and has a hardness of 2. Crystals of silvite are colorless if pure, however often they're reddish in Bages because the content of iron oxides. Silvite is easily identified by its spicy taste, more or less bitter according to its amount of carnalite (hydrous magnesium and potassium chloride) traces. Silvite is exploited in mines of potash nowadays in Súria, Balsareny and Sallent and, until 1990, in Cardona as well where the mine achieved -1000 m depth. In plain, unfolded areas, silvite is found in two layers, 100 m below the top of the Cardona formation. Usually, centimetric sheets of silvite and halite are blended. Then the rock is called silvinite. The word potash means any potassium containing sedimentary rock. Silvite is used mainly in fertilizers. In the photography, the appearance of a just mined mineral: a mass of tiny, orange crystals of silvine that is crossed by a layer of colorless halite crystals.
 |
CARNALITE (KMgCl3·6H2O,
hydrous magnesium and potassium chloride)
Carnalite crystallizes in rhombic system and has a hardness of 2.5, the same as the nail. It usually displays granular structure. Carnalite can be colorless, pinkish or reddish, always with a vitreous gloss. Carnalite is deliquescent, it solves even in the air humidity. Its taste is salty, spicy after the potassium and bitter after the magnesium content. In the sequence of the Cardona geological pack, carnalite is found in a higher position than silvine. Thus, carnalite is the first potassium mineral that appears, however its presence is irregular.
The water streams have opened natural caves in three types of rock in Bages: in conglomerate in the mountain areas of St. Llorenç del Munt i l'Obac and Montserrat, in marine limestones in El Toll (Moià) and in salt in Cardona and beneath Sallent. In addition there are mine galleries for salt or potassium explotation below Cardona, Súria, Sallent and Balsareny.
In the two mountain areas of conglomerate, Sant Llorenç del Munt i serra de l'Obac and Montserrat, the previous vertical crevaces network and the softer layers of clay drive the water circulation beneath the surface. After that, the dissolution of the carbonated concrete by karst process generates cavities, whether caves, vertical shafts or just rock roofs. The highest number of cavities in Bages belongs to the conglomerate rock type.
 |
In the larger area of Sant Llorenç del Munt i l'Obac massif there are many caves. Amongst them, the cave of Mura stands out by the beauty of its internal formation. The cave of Simanya, near to Mountcau peak, is the most visited because of its convenient access. In L'Obac range there are the shafts of El Llest and Castellsapera, both with big entrances, and those of Sant Jaume de la Mata and L'Espluga which is the dippest one with -127 m. The Puig de la Balma (Mura) is a building from XII century that takes advantge of the natural rock roof.
 |
The biggest and the most beautiful cave in Montserrat is certainly that of Salnitre. It's located in the south slope, in Collbató (Baix Llobregat), together with caves Freda and Gran. The cave of Salnitre shows an ancient water drainage of the massif. The Mentirosa spring of Monistrol is an usually dry cavity close to the road to the monastery. However, from time to time after heavy rains, there is a big, powerful water spring from Mentirosa cavity. Main shaft in Montserrat is Els Pouetons, -123 m dip. It's located in the area that's called Agulles , so the neddles or pillars.
  |
In Moià, there is the complex of caves of El Toll into marine limestones. They were originated by a plenty of water stream. Then, mud laid on the caves galleries. In addition to the sediments, the entrance to the main gallery of cave of El Toll was completely covered by a landslide some thousands of years ago. The careful dig of these sediments provided a lot of bones and fossil remains of the living in the area animals ranging since the period of first Würm glaciation (100.000 year ago) to nowadays. Some of these animals became extincted. Some of them were also really big and frigthening, like the lion (Panthera spelaea (†)), the bear of the caves ( Ursus spelaeus (†)) and the rhinoceros of Merck (Stephanorhinus mercki (†)). In addition, the complex of caves of El Toll has provided archeological rests of the human presence in the middle Paleolithic (50.000 years) and mainly in the Neolithic. The findings from the excavation campaigns in the caves of El Toll are presented in the Museum of Archeology and Paleontology of Moià.
 |
Furthermore, there is the rare carst in salt rock in Bages district. Only the salt cave Forat Micó in one side of the salt mountain of Cardona is known for a long time. It's 640 m length and some of its walls are decorated with delicate crystalls of halita. But the mining in second half of century XX changed the scenario of Cardona. Galleries were mined into the salt mountain and salt residues were thrown over the valley. The hydrologic balance was disturbed. As a result, the water suddenly opened new channels, a new endo-karst process into the salt environment broke out. The common salt is much more soluble than any other so-called soluble rocks that are able to sustain a karst process, like limestone or conglomerate that also provide caves in separated areas of Bages district. One liter of water solves 357 g of salt to become saturated brine. In just several years, water flowing through abandoned galleries has reshaped them and has opened new cavities into the bottom of the salt mountain of Cardona. Recent cavities are the long cave of Meandres de Sal (salt meanders) 4300 m length, the cave of El Riu (the river), a salt water lake beneath the surface and the cave of Rierol Salat (salt stream), the last one into the old salt residues dumpfill. The sudden carst process in Cardona salt was growing with chaotic collapses on the surface. It was threatening the feasibility of a salt mine –which to some extent was responsible for the out of control water- and even the chance of pulling the whole river Cardener and sending it to the deep mine. The uncertain, chaotic circumstances lead to the deviation of river Cardener through a tunnel in order to move it away from the salt area. The research of Espeleo Club de Gràcia has reported and outlined the new born endo-carst into the salt mountain in Cardona.
There is a big cave beneath L'Estació (Sallent) which is in contact with the old potassium salt mine Enrique. Finally, other endo-carst into salt environment may be found or can develop into the salt dumpfills, specifically in the abandoned ones like in La Botjosa (Sallent).
The caves of El Toll (Moià) and Salnitre (Collbató) as well as some mine galleries into the mountain of salt of Cardona are open to tourism.
Fossils are material proofs of living organisms in the geological past. They are usually found into sedimentary rocks. They allow to know the age of these rocks and the environmental characteristics of the area when these organisms were alive. The source of the most common and known fossils in Bages is the sea. They come from the living organisms of the former, not too much deep, warm sea that covered the region during most of the Eocene period. Fossils can also be found in rocks of lake origin. Fossils of terrestrial vertebrates from quaternary period have been dug up in fluvial terraces (i.e. elephants) and in Toll caves (coves del Toll) in Moià (i.e. bears, hyenas, rhinoceroses.).
I
n terms of Geology, the fossils of Bages are recent , thus most of them are similar to the current species.
Hereafter, there is a description of the fossil groups that are common in Bages. However, in the area there are also fossils of vegetable remains, sponges, bryozoans, worms, crabs, shark teeth, turtle shells, sirenid bones.
 |
NUMMULITES
Nummulites are one of the most typical fossil groups of the marine Eocene. Their popular name is lentils or coins, because of its shape like a lentil. In some places of Bages, they outcome detached in loamy plots of land where they can generously be collected. Also nummulites are the main component of a compact rock: the Sant Vicenç limestone which is actively exploited as stone for ornamental and construction purposes.
Nummulites became extinguished at the end of Oligocene. They were giant marine protozoans -from few millimeters till 6 cm diameter- of the faraminifer group, with the body covered by a calcareous shell. The studies of the nummulites by Dr. Valentí Masachs contributed to to date the different levels of the Eocene of the region.
 |
CORALES
Corals are colonial marine animals that secrete a calcareous skeleton. Coral reefs, this are the big, calcareous, submarine buildings that are almost made by the skeletons of these animals and where life shows a peak of high biodiversity, growth only in clear, low mineral nutrients containing, warm sea waters (minimum winter temperature higher than 15ºC). The fossil coral reefs outcome in line from north-east to south-west in Bages. They proof the past tropical climate in Catalonia along the Eocene. The fossil fauna of the coral outcrops in Bages (Manresa, Navarcles, Calders.) is quite similar to that of the current coral reefs.
 |
BIVALVES
Bivalves (shells, mussels, oysters.) are mollusks provided with a calcareous shell of two valves that are inserted by a hinge. During the Eocene, a lot of bivalves lived in the muddy sea bed close to the coast and to the fluvial mouths. The best preserved fossils of Bivalves belong to the families with thicker and bigger shells. Fossils of families with thinner shells are often just their external or internal moulds.
 |
GASTROPODS
The diversity of fossils of gastropods (snails) is noticeable in Bages. Their shapes vary from shells with just few turns (Velates, Natica, Terebellum) to very twisted shells (Turritella, Melanoides) and to giant snails (Campanille, Cerithium).
Most of gastropods fossils that are collected in Bages lived in the sea. However, the snail on the photo is one among the few fossils that are found in the layers fom continental lake origin. rocks.
 |
ECHINODERMS
Sea urchins are the most frequent echinoderms in this region. They are strictly marine invertebrates. Sea urchins have an external, calcareous skeleton that is made by welded plates and protuberances where prongs are articulated. They are one of the most attractive fossils of Bages, because they are usually entire and well-preserved. Their shapes are more or less globular or flattened, with radial or bilateral symmetry.
[Oriol Oms, Florenci Vallès and Josep Biosca, with the collaboration of Jordi Badia and Joaquim Sanz]
