290 



THE GEOLOGIST. 



through Worsley^ Bury, Burnley, &c. to the limestone shales 

 of Pendlehill, there are 36 seams, only ten of which are less 

 than one foot in thickness, amounting to 93 feet of coal; in 

 these sections the smaller seams are not taken into account. 



I. Roofs, The deposits forming the roofs vary in dif- 

 ferent places^ even over the same seam. There are four 

 kinds of roofs. 



1. A fine mixture of alumina and silica, with oxide of iron, 

 and a trace of the carbonates of iron and lime ; these are 

 generally known as blue binds, and are of most frequent oc- 

 currence ; they almost always contain ferns, and remains of 

 Stigmaria, Sigillaria, Ulodendron and Lepidodendron, and 

 beds of the Unio and other shells. The Sigillarise are by 

 far the most common; at Pendleton and Dixon-fold they 

 occur as abundantly as they could possibly have grown : the 

 author had observed three specimens at Pendleton, 24 feet 

 high, and about 3 feet in circumference, standing in a shaft 

 1 1 feet in diameter. 



2. Roofs of Sandstone are not common^ and where they do 

 occur the coal is generally inferior in quality; the fossils 

 found in the sandstone are usually prostrate coal plants, 

 Stigmariee, &c. 



3. Black shale roofs are frequent, and cover most of the 

 best house-fire and caking coal ; they seldom contain plants, 

 though, in a few instances, upright Sigillariae have been 

 found. Bivalve shells, detached scales and teeth of fish fre- 

 quently occur in them, and with the Microconchus carbonaskis 

 and casts of Cyprides sometimes constitute nearly the entire 

 mass ; almost all the black shale roofs of the lower field teem 

 with remains of Pecten, Goniatites, Posidonia, and remains 

 of fishes. 



4. Shales with highly bituminous schists, forming roofs, are 

 not of frequent occurrence; they are found at Peel and 

 Pendleton, and contain abundant remains of fish, mostly 



