6 



its southern boundary, and the sea its northern. It adjoins the province 

 of Biscay on the east, and that of Asturias on the west. The first range of 

 the chain forming the southern boundary of the province, which at 

 Puente Yiesgo is only a few miles from the coast (four leagues from San - 

 tander, the chief town), is chiefly formed of mountain limestone. Upon 

 this rock rest beds of red sandstone, and ochry clay, with accompanying 

 gypsum ; these are succeeded by shelly limestone, sandstone, and clay, 

 irregular beds of limestone, and dolomite, some of which yield an ex- 

 cellent cement. Upon these rocks rest beds of shelly limestone, and of 

 dolomite, the former containing abundance of a large species of ostrea, 

 and of terebratulae and ammonites. Above these, on the sea- coast, 

 tertiary limestone and sandstones are found. The rocks which thus 

 occur between the mountain limestone and the tertiary beds apparently 

 represent the two lower groups of the triassic period — the bunter sand- 

 stone and the muschelkalk. For the moment this opinion is little more 

 than a guess ; but we hope to be able to establish the true relations of all 

 those beds, when we have collected the materials for a memoir upon 

 the geology of the entire district, with which we propose to occupy 

 ourselves. 



In the mountain limestone at Yiesgo are found galena, blende, car- 

 bonate of zinc (Smithsonite), copper and iron pj^rites, with here and 

 there deposits of gypsum. The hot baths of Viesgo, Las Caldas, and 

 Thermida, indicate the Jprobable proximity of igneous rocks, or, at all 

 events, the existence of conditions favourable to metamorphic action. 

 Indeed, the limestone in the immediate vicinity of a lead lode which 

 occurs in this rock is hardened into marble. The lodes occur gene- 

 rally not far from the line of junction of the limestone with the red 

 sandstone. In the soft steatitic clay which is found in the lodes, abun- 

 dance of doubly terminated crystals of clouded quartz are found. Small 

 crystals of the same kind, imbedded in a paste of peroxide of manganese, 

 likewise occur in the lodes. There is, indeed, everywhere in the dis- 

 trict, evidence of the presence of large quantities of silica in solution, 

 in former times. The vein stone is sulphate of barytes, or calcite ; the 

 latter is frequently found in large crystals, of the form of a scalenohe- 

 dron (the metastatique of Haiiy, of Levy and Dufrenoy, and S3 of 

 Zippe). 



Ores of zinc likewise occur in the newer or triassic rocks. Their 

 chief seat is the dolomite, which, if our surmise be correct, belongs to 

 the muschelkalk, and suggests analogies with the zinc deposits ofWies- 

 loch in Baden. The ores which occur are blende, often galeniferous, and 

 carbonate (Smithsonite), the latter being most abundant. The lodes 

 are usually vertical, traversing the dolomite nearly at right angles, and 

 presenting generally merely the elements of a lode or vein, namely, a 

 plane of fracture with some foreign matter interposed, which, as in the 

 mountain limestone, is usually sulphate of barytes and calcite, the 

 small rhombohedral crystals of the latter being in some places altered 

 into sulphate of barytes. In some cases, as will be noticed presently, 

 the calcite is replaced by carbonate of zinc, which forms beautiful pseu- 



