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TRANSACTIONS OF THE 



pondence or parallelism between the upper and lower 

 surfaces of the main coal seam ; neither does its roof pre- 

 sent the usual continuity of plane as is seen in ordinary- 

 stratified deposits. 



But in those lower thick seams, under our immediate 

 consideration, the roof is irregular, rising and falling, 

 swelling and expanding, without at the same time con- 

 forming to the undulations of the granite base ; the de- 

 pressions in the roof occasionally descending towards ele- 

 vations of the floor, and the contrary. 



Amidst this irregularity, it must be observed, there is 

 no important interruption to the parallelism of the lami- 

 nae or planes of stratification within the body of the coal 

 itself. So far as my examination of these beds in the 

 deep workings extended, the laminse or their seams, of 

 which the whole mass was made up, were of uniform 

 thickness, parallel with each other, and with the prevail- 

 ing dip of the coal. 



The hard dry shale which forms chis roof is not lami- 

 nated or seamed like the coal shales higher up : but, 

 wherever it has come under my observation, it possesses 

 the polished conchoidal glance cleavage, which is more 

 characteristic of the transition coal measures than the 

 secondary. This is one reason, although not altogether 

 conclusive, why I am rather inclined to assign this inde- 

 pendent coal formation among the transition carbonifer- 

 ous deposits, than to the secondary class, wherein I can 

 trace no analogy throughout the whole series of superin- 

 cumbent strata. 



That the alternative of bituminous or non-bituminous 

 has no authority in determining the comparative ages of 

 coal, I have shown in a previous article on the bitumi- 

 nous transition coals of Pennsylvania. 



In the formation now under consideration, we perceive 

 not a single bed, out of a series occupying 700 feet at least 



