STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 489 



that detailed study is not possible in a considerable part of the area. 

 The Coal Measures have an area of about 540 square kilometers in 

 the Asturias and the principal basin is the Central, or Sama de 

 Longres, containing not less than one third of the whole coal area ; 

 other basins are smaller, but in some cases are economically im- 

 portant. 



The Assise de Leiia receives its name from Pola de Leiia, north 

 from the Cantabrian Mountains, where the succession is well shown. 

 It is exposed b}^ an anticline in the Central basin, where its character 

 is distinct. Near the montee de Cardeo in that basin, is a conglom- 

 erate belonging to this assise, which has aroused much discussion. 

 It consists of large quartz pebbles, grayish white, which are marked 

 in such manner that each observer has felt compelled to offer some 

 explanation ; some have regarded the phenomenon as due to chemical 

 action, others think it due to pressure, to heat, etc. Barrois would 

 explain it as due to wind agency. The sandblast produced by winds 

 has had marked effect on quaternary pebbles in the Rhone Valley. 

 Similar blasts could have polished or striated the pebbles of this con- 

 glomerate as they lay exposed on a beach. The coal seams of this 

 assise are without economic value. 



The Assise de Sama or lower division of the terrain houiller 

 riche of former observers, is the important group of deposits in the 

 Central basin. Coal seams are shown in one section associated with 

 shales and sandstones containing impressions of Calainites and Stig- 

 maria with nodules of clay ironstone; the coals rest on soft sand- 

 stone or shale filled with Stigmaria. Near Padrun is a conglom- 

 erate containing pebbles of coal, 4 to 5 centimeters in diameter. Oa 

 Rio Caudal there appear to be about 30 seams of coal, arranged in 

 groups which are separated by barren intervals. The mur usually 

 is a compact shale crowded with Stigmaria and fragments of plants, 

 but the toit has abundant beautiful impressions. A faux- toit, lO' 

 to 15 centimeters thick, consisting of shale and coal, often covers 

 the coal and at times is pulverulent. Barrois determined that the 

 number of coal seams reported by earlier observers is far too great 

 and that those who reported 72 to 80 seams failed to recognize sev- 

 eral folds ; he intimates that most probably the number is too great 

 by at least one half. Throughout this basin, seams show much 



