490 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



variation in thickness, some, at times, thinning away to disappear- 

 ance. One seam attains 3 meters ; in one case coal only 30 centi- 

 meters thick is mined. Coals of the same age are in the small 

 Santo-Firme basin, where the formation, resting on the Devonian, 

 is about 500 meters thick and contains 10 coal seams. It underlies 

 post-Carboniferous rocks. The coals show the usual tendency to 

 vary in thickness, sometimes thinning away only to reappear within 

 a short distance. A marine shale, rich in fossils, is roof of a coal 

 seam in upper part of this assise. 



The Assise de Tineo is confined to some small basins in the west- 

 ern and to two in the northern part of the old kingdom. In Tineo 

 basin these rocks rest on the Cambrian. In Arnao and Ferrones 

 they rest on Devonian and, because of faults, appear to be inter- 

 calated in rocks of that age. The basins of Ferrones has but one 

 coal seam and the overlying Devonian contains fine fossils. 



The province of Oviedo had 210 mines in 1869. Studies by de 

 Aspiroz and by Paillette proved that the composition of the coal is 

 not the same in different basins and that it varies even in the same 

 assise. The most of the coal is bituminous but a maigre, anthra- 

 'Citic coal is obtained in Vinon and Calunga basins ; this, of no value, 

 may belong to the Assise de Leiia. Volatile in the Central basin, 

 belonging to the Assise de Sama, is 30 to 45 per cent, and the ash is 

 from .04 to 3 per cent. But these are only of selected specimens. 

 Coals from the small northern basins have theoretical interest. 

 These give, according to analyses by Paillette: 



The Santo Firme coal belongs to Assise de Sama, that from Arnao 

 •and Ferrones, to Assise de Tineo. The difference in volatile might 

 be attributed to the age of the coals, Santo Firme, the older, having 

 less volatile; but Barrois thinks that another explanation, more 

 satisfactory, may be found in the relation of composition to strati- 



