Obsercations on the Occurrence of Anthracite.— Gresley. 9 
doubtless they were originally part of the same series of beds 
much more extensively preserved in the southwest corner of 
Pennsylvania. 
3. We have already seen that the Coal Measures of the re- 
gion in question are characterized by strata of sandstone, 
grit and conglomerate; shale and clays being comparatively 
unimportant, limestones still more so. 
4. There can be no doubt but that as these Coal Measures 
were deposited by and in water they would be saturated there- 
by as the area of deposition subsided, and so would retain 
most of the water, just as the gravel beds, quicksands and 
sands do in estuaries and in valleys, or as the porous breccias, 
conglomerates and sandstones of the Permian and Triassic 
series in many European localities are heavily watered. 
5. The coarse character of the strata implies a not distant 
coast or shore line or land, of course undergoing waste b}^ 
erosion and denudation. Proximity to the shore coupled 
with coarseness of sediment also implies a relatively thicker 
vertical pile or series of (Joal Measures than would be 
deposited further offshore and in deeper water and charac- 
terized by rocks of finer grain. The Pennsylvania Geological 
Survey computes the vertical thickness of C'oal Measures in 
the center of the southern anthracite basin at about 4,000 
feet, and for all we know this thickness was probabl}' greater 
once, even greater further to the east and northeast. 
6. The greater the vertical thickness of strata laid down in 
practically uniform succession one above another, the greater 
the subsidence of the area of deposition. 
7. Strata-building must come to an end somewhere — some- 
time ; and in the case of the Pennsylvania coal-area it is liigiily 
probable it ended with the Permian age, in other words tiie 
topmost or last-formed bed of that series (wherever it 
may have been deposited) was the proverbial straw that 
broke the camel's back; that is to say the weight and subsi- 
dence of the Paleozoic rocks iuid by that time become great 
enough to bring them witiiin the limits or zone of suHlcient 
interior earth-heat to produce a softening of them accom- 
panied by some swelling or tendency to swell. The absenct- 
of Permian and' Triassic rocks over the Coal Measures toward 
Ohio, Indiana, Missouri, and still farther west, and from what 
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