No. 200.] 
mi 
telligible; from their well defined configuration, and from being one of 
the terminal or extreme western limits of those great derangements 
whose cause has acted with so much violence along the whole of the 
Atlantic region of the United States, and from a number of highly inte- 
resting phenomena, are admirably calculated to instruct the student of 
geology in the knowledge of some of the proximate causes of the varied 
appearance of the surface of the earth and the derangement of its strata. 
Here, too, they form laboratories for knowledge, and not manufactories 
of mineral wealth, as we find they do in similar but more extensive, 
though more obscure, positions further south. 
It may be supposed that in thus treating the subject I have trespassed 
beyond the bounds of the annual reports, but so necessary is the know- 
' ledge of these uplifts to show the cause of the derangement of the sur- 
face of the counties where they exist for practical purposes, that had 
they no other foundation than was required for illustration they were 
admissible; but as matter of fact and matter of utility their omission 
would have been inadmissible. 
MONTGOMERY COUNTY, 
The whole area of this county, with perhaps a small portion to the 
southwest, which I had not time to examine, lies to the north of the 
great elevation, and therefore contains a less number of rocks than the 
counties of the west through which the great elevation extends. Gneiss, 
calciferous sandrock, birdseye, Trenton limestone, black shale and the 
rubblestone of Prof. Eaton, with green shale in small quantity, were 
the only rocks met with in Montgomery county. 
The order of the arrangement of these rocks is invariably the same. 
There may be exceptions to the casual observer, but the exceptions are 
merely apparent, arising from the uplift, by which a lower rock is placed 
upon the same horizontal parallel with an upper one, but when the rocks 
of the uplift are examined, they invariably show the same series in the 
order enumerated, though often one or more of the upper members are 
wanting, owing to denuding action, of which other facts bear ample 
evidence, no part of the third district yet examined, having been ex- 
empted from destructive agents, especially the erosive action of water. 
The rubblestone, with its green shale, occupies the whole of the 
southern border of the county, being the upper rock. When fresh 
quarried, it is of a blueish green colour, but becomes of an olive by long 
exposure to the air. It appears to stand weathering, for all the nume- 
rous enclosures met with in that part of the county are formed of this 
[Assem. No. 200.] 29 
