J:24 GEOLOGY, 



to examination, variously curved and folded, together, so as in many in- 

 stances, as at B, to be almost folded back upon themselves. It will be 

 seen that the curvature or foldings of the strata are greatest on the east, 

 and con.stantly diminish as we proceed westward. At C, the uppermost 

 stratum, which is that containing coal is nearly perpendicular to the hor- 

 izon, whilst at F and D, where it re-appears again, after having been 

 wanting between C and D, it is nearly horizontal. Hence we find, that 

 whilst the coal beds in Eastern Pennsylvania are highly inclined to the 

 horizon, those of Western Pennsylvania and farther west are nearly hor- 

 izontal, and are worked by carrying tunnels or horizontal galleries into 

 the sides of the hills, along which the coal crops out or appears at the 

 surface. 



Now this shattering, turning up on their edges, and curving and fold- 

 ing of the successive strata of rocks, if they were not placed in their 

 present position at first by the hands of the Creator, give evidence that 

 they must have been subject to some violent disturbing force from be- 

 low, and that this force must have operated most violently on the east 

 and diminished in intensity in the west. Nor is this disruption and 

 bending of strata peculiar to the Eastern United Slates, but it is found ev- 

 ery where, in all countries over the globe, and is one of its most general 

 features; so that if a disturbing cause existed, it has had a very wide 

 range of operation. After the question, whether these strata give any 

 internal evidence that they have not always existed in their present form 

 and position, shall have been disposed of, it may be proper to inquire' 

 into the causes which have been instrumental in producing changes. 



4. Another circumstance, which cannot fail exciting our interest, is 

 that the stratified rocks afford the strongest evidence that they were, all 

 perhaps without exception, formed or deposited in succession by water. 

 On this account they are often called sedimentary rocks. 



First., their occurrence in strata affords a strong presumption in favor 

 of this view. Tiiey could be deposited in successive strata only I'rom a 

 fiuid state; the materials having either been fused by fire, or held in sus- 

 ])cnsion by water. Their structure, and the organic remains or fossils, 

 which many of them contain, afiord proof sufficient that they had not 

 been rendered fluid by fire, but by water. 



Secondly., the higher rocks often contain or are made up of the frag- 

 ments of those which lie below them. Some are made up of the angu- 

 Ly fragments of previously existing rocks. Such is the character of 

 the Limestone Breccia, which seems to occupy the angle formed, at the 

 Eastern base of the South Mountain or Blue Ridge, by its highly in- 

 clined strata witli the slightly inclined strata d the adjacent red shale and . 



