Palfpozoic Jlhfoi'ii of P(^n7)sylvania. — Chiypole. 153 
A similar departure from the type occurs in middle Pennsyl- 
vania. There, in Perry county for example, the Hamilton com- 
prises a lower shale followed b}' a massive sandstone on which lies 
•an upper shale closely resembling the lower in texture, material 
and general appearance. No limestone is present. 
The section therefore in detail is as follows : 
Hamilton upper shale 250 feet 
" sandstone 800 " 
" lower shale 4.50 " 
1,.500 " 
The intercalation of this enormous mass of hard sandstone in 
the Hamilton group gives it a strange aspect to one onh' accus- 
tomed to see it as it appears in New York. As may be inferred it 
changes the character of the surface where it ci-ops out from a 
gentle rolling rounded contour to one, rough, wild and wooded 
and generally incapable of cultivation. 
This sandstone prevails over several counties but reaches its 
maximum thickness in Perr}- Co., where it is thus described in the 
writer's report (Fo of the Geological Survey of Pennsvlvania). 
"The Hamilton sandstone is one of the most remarkable formations 
of Perry county. Lying in the midst of a vast mass of shale it has the 
appearance of being out of place to the geologist accustomed to look on 
the Hamilton as essentially a soft group. 
"It forms numerous mountains in the county, Turkey ridge, Buffalo 
ridge, Mahanoy ridge, Dick's hill with its continuation, Rock hill, also 
Pisgah hill and Little mountain are all formed by outcrops of this sand- 
stone. Some of these are high, rough and untillable ; others are com- 
paratively smooth and accessible. This difference is due to two causes 
— the hardness and the dip of the sandstone. The proportion of sand 
also rapidly diminislies to the north and west especially in the middle 
of the bed, diminishing the steepness and roughness of the ridges. 
"At its southeastern exposure near Marysville this sandstone attains its 
greatest thickness and hardness — a thickness amounting to 800 feet. 
From this point it gradually thins away, the upper and lower beds per- 
sisting farthest and the intermediate shale becoming constantly thicker 
until at length it becomes two distinct sandstones with an intervening 
bed of softer material. This change may be detected iu Perry county. 
At Montebello Narrows the Little Juniata has cut its way through the 
lower beds and has then (lowed for nearly half a mile parallel to the 
ridge and between the two saudstones, at length crossing the upper and 
thus producing a zigzag channel. But outside the limits of the county 
the change becomes more manifest. At and near Huntingdon the two 
sand layers may be distinctly traced only a few yards thick, the upper 
toeing the heavier. The great mass of the bed has become siialv. This 
