INTRODUCTION. 30 



By tracing the direction of these geological formations on the east 

 and west, we cannot fail to observe a convergence to the southward ; 

 and it is there, if at all, that facts are to be obtained that will show 

 conclusively the relative age or synchronism of these formations lying 

 between the Coal measures and the Chemung group. 



At the commencement of the Coal-measure deposits, we find a return 

 to those conditions which have prevailed during all the preceding 

 important sedimentary groups. This formation exists in Nova-Scotia 

 and New-Brunswick, and again in Pennsylvania, stretching southward 

 into Alabama ; while to the west it extends with slight interruptions, 

 but with diminishing thickness, far beyond the Mississippi river. 



The thickness of this formation in Nova-Scotia, according to the 

 careful measurements of Sir William Logan, is more than fourteen thou- 

 sand feet. In Pennsylvania, Professor Rogkrs states it, including the 

 conglomerate, at more than eight thousand feet*. Taking these as 

 initial points, and carrying our observations to the west and southwest, 

 we find a constantly diminishing thickness in that direction, and finally 

 the entire formation is represented by a few hundred feet of strata. 



The measurements of Professor Swallow, in Missouri, give six hun- 

 dred and forty feet as the thickness of the Coal measures proper; and 

 in Iowa the amount is still less. 



The great Conglomerate which lies at the base of the formation, and 

 in Pennsylvania measures fourteen hundred feet, appears in considerable 

 force in Ohio and in Indiana, but has entirely thinned out before 

 reaching the Mississippi river. Of the other members of the formation, 

 the coarser materials have diminished, and the Coal measures in the 

 west are composed of finer sediments than in the east. 



Thus we see everywhere the operation of the same law, viz. a greater 

 accumulation, and a coarser character of sediments along the line of 

 the Appalachian chain, with a gradual thinning to the westward, and 

 a deposition of the finer or far transported matter in that direction. In 



• Even sdmitting, as has been claimed by some, that this thickness is over-estimated, a difiercnce 

 of one or two thousand f«et would not affbct our general conclusions. 



