418 [May 15, 



glomerate subordinate to it, and it may, with all probability, be 

 referred to the old red sandstone which occurs beneath the coal 

 in Pennsylvania ; although, in the absence of fossils, the dis- 

 turbed state of the strata, and the frequent concealment of their 

 outcroppings by a thick covering of drift, it is usually difficult to 

 determine the exact order of succession. It is, however, important 

 to observe that the whole of this series, which Professor Hitchcock 

 now inclines to refer to the coal and old red sandstone, was for- 

 merly called greywacke, and styled the transition formation, in 

 consequence of the semi-metamorphic condition of several of the 

 rocks. Their conversion into crystalline strata, in the immediate 

 neighbourhood of masses of granite and syenite, is often complete. 

 But besides this kind of alteration, resembling the effect of dykes 

 and v^ins of intrusive igneous rocks, there is evidence here, as in 

 the Alps of the Canton of Berne and elsewhei'e, of a more exten- 

 sive and general change by chemical or plutonic action, affecting, 

 with greater or less degrees of intensity, dense masses of stratified 

 rocks. 



Altliough many impressions of plants have been found in this 

 anthracite formation, on the southern borders of Massachusetts and 

 Rhode Island no traces of shells or corals have been discovered. 

 In like manner we find an absence of all fossils except vegetable 

 remains, in the anthracite coal district of Pennsylvania, and no 

 fossils of any kind in the subjacent conglomerates and red sand- 

 stones. 



The strata of conglomerate at Brooklyn, near Boston, and the 

 greywacke slates and sandstones of that neighbourhood, some of 

 which pass into metamorphic rocks, and in which no plants or 

 other organic remains have as yet been found, are doubtless refer- 

 able to the same carboniferous and Devonian formations as those 

 above described. 



After traversing this region in several directions, it appeared to 

 me very probable that the stratified rocks, containing the plumba- 

 ginous anthracite of Worcester, consisted originally of similar 

 sedimentary strata, which have been so altered by heat and other 

 plutonic causes as to assume a crystalline and metamorphic texture, 

 by which the grits and sliales of the coal have been turned into 

 quartzite, clay-slate, and mica-schist, and the anthracite into that 

 state of carbon which is called plumbago or graphite. 



The progressive debituminisation of the coal of the United 

 States, as we proceed from Pittsburgh to the eastern and more dis- 

 turbed axes of the Alleghany mountains, as pointed out by Pro- 

 fessor H. D. Rogers, lend support to this conjecture.* In the 

 Rhode Island anthracite, which is less combustible than that of 

 Potsville, Pennsylvania, the change seems to have been carried far- 

 ther ; the volatile ingredients of the original coal having been still 

 more completely expelled. In the impure plumbago of Worcester, 

 we may have the last step in the series of transmutation, where only 

 3 per cent, of gaseous matter remains, where all traces of fossil plants 



* See Appendix. 



