20 EXPEDITION TO THE 



nates without any interruption. It consists merely of al- 

 ternating strata of slate-clay, sandstone, limestone, and coal. 

 Of these the sandstone is the most abundant ; it is generally 

 fine-grained, composed principally of fragments of quartz, 

 connected by a siliceous cement. In some cases there is 

 much mica, and at times a little feldspar, so as to consti- 

 tute in local formations a regenerated granite not unlike 

 that observable in the coal basin of St. Etienne in France, 

 but these are rather mineralogical curiosities, and can 

 scarcely be considered as forming a feature in the geology 

 of this part of the route. The stratification is nearly hori- 

 zontal, and is very distinct wherever the slate-clay is found, 

 but wn^re this rock is deficient, the sandstone loses its 

 stratified character, or at least ceases to present it in a dis- 

 tinct manner. 



The sandstone frequently alternates with the slate-clay, 

 and it is not uncommon to observe a real passage of the 

 one into the other ; in some cases, as in the neighbourhood 

 of Cumberland, the slate-clay is very rare. 



The limestone is compact, of a grayish or brownish co- 

 lour, very argillaceous, emitting a strong argillaceous 

 odour when breathed upon ; it occurs in parallel stratifica- 

 tion with the above-mentioned rocks, and exists very 

 abundantly all over the country, where it may be seen in 

 many places alternating with the other strata ; but we know 

 of none where this can be so well observed as on the west 

 bank of the Monongahela, in the neighbourhood of 

 Brownsville, in those places where the road has been dug 

 into the hill. 



The coal has not yet been found to the eastward of 

 Cumberland, but west of this town it occurs almost every 

 where; it is found in beds which vary in thickness from 

 an inch to several, sometimes ten, feet. It appears that 



