Stevenson.] ^oi [Dec. 18, 



every attempt to tabulate tliem was a failure. For many years the re- 

 ports of all observers led us to accept the divergence or convergence of 

 coal seams as part of the necessary arrangement of things, a phenomenon 

 quite as ordinary as the occurrence of sandstone or shale in the inter- 

 vals. 



Quite recently, Prof. E. B. Andrews, an assistant on the Ohio Survey, 

 has re-asserted the parallelism of coal-beds, and admits of such excep- 

 tions only, as result from the greater or less compressibility of the ma- 

 terials occupying the intervals. He concedes, it is true, that when large 

 areas of any coal field are examined, it may be found that some portions 

 have had a more rapid subsidence than the rest ; but he maintains that 

 as a rule the subsidence was so regular that two seams are found to pre- 

 sent an almost perfect parallelism. He doubts whether it is possible for 

 a seam to separate into two or more parts, or if separated, for the parts 

 to diverge indefinitely, that is to say, I suppose, for several miles hori- 

 zontally or to any great extent vertically. 



This is no matter of merely theoretical interest. Involving, as it does, 

 not merely the whole question respecting the deposition of coal seams 

 and the intervening rocks, but also, as a consequence, the identification 

 or tracing of the beds over extensive areas, its exact determination is 

 equally important to the economic investigator and to the purely scien- 

 tific student. It is true, that the question has been a settled one for many 

 years, but long acceptance of a doctrine does not prove its truth. It has 

 been disputed by a Geologist of standing, whose statements deserve and 

 receive consideration. There is need then, that the matter be presented 

 in such a manner as to leave no doubt in the mind of any that the idea of 

 parallelism over even limited areas is utterly fallacious except for rare 

 localities. In geology an erroneous theory is of necessity a pernicious 

 theory. 



Coal seams do divide. That is to say, the numerous partings in a coal 

 bed are liable so to thicken as to become distinct strata of shale or sand- 

 stone, and in many cases they do so thicken. In his memoir upon the 

 South Staffordshire Coal Field, Prof. Jukes gives an illustration, especial- 

 ly interesting because of the ease with which the bifurcation of the vari- 

 ous seams is proved. The coals begin their separation in the southern 

 portion of the field and the divergence continues northward, the coals 

 never coming together again within the area embraced in the memoir. 

 In Plate 1, Prof. Jukes compares two vertical sections, one taken in the 

 south-central portion of the field, and the other in the north- central por- 

 tion, the distance between them being about five miles. In the first sec- 

 tion, which represents a vertical thickness of 350 feet, thei'e are seven beds 

 of coal, each made up of several distinct layers separated by their part- 

 ings. In the second section, whose thickness is 850 feet, there are 

 eighteen beds of coal, some simple, but most of them compound. The 

 character of the coal from the several seams in the second section shows 

 at once the relation to the bsds of the first section. 



