Geology and Mineralogy. 303 



Rogers that the anthracite is due to metamorphic influence of 

 steam and superheated gases escaping from crevices : that of J. P. 

 Lesley that the metamorpkism is due to increased earth heat: 

 and the other that the metamorphism is due to transformed 

 mechanical force were examined and in each case found to be 

 unsatisfactory, being either discordant with the facts or unsup- 

 ported by them. The author maintained that the coal is not due 

 to metamorphism but to longer continuance of the process whereby 

 bituminous coal is formed. Twenty years ago he was led to 

 believe that the great coal marsh, which was the parent of the 

 successive coal beds originated at the east, and after each subsi- 

 dence advanced seaward once more upon the new deltas. Under 

 such conditions the thickness of coal in the northeast corner of 

 the Appalachian basin, where the deltas formed rapidly, should 

 be very much greater than in any other portion, and therefore the 

 degree of conversion should be greater there than elsewhere. 

 Comparisons of the several groups of the coal measures show 

 that in the anthracite strip the thickness increases northward 

 slowly until beyond the southerly prong of the southern anthra- 

 cite field ; but that the increase is abrupt at that point and soon 

 becomes very great ; also that the thickness of coal decreases 

 westwardly as the distance increases from the anthracite region. 

 Comparison of analysis shows' that the amount of volatile matter 

 decreases toward the anthracite region, toward the region of 

 greatest thickness of coal ; and that the decrease is gradual, 

 even in the anthracite strip, until the thickness increases abruptly. 

 It was shown that the decrease in volatile material has no rela- 

 tion whatever to increase or decrease of disturbance in the rocks : 

 that it is wholly independent of the general composition of the 

 associated rocks : that it is not due to the influence of heat as a 

 metamorphic agent: but that it is due to longer exposure, prior 

 to entombment, to conditions favoring the escape of CH 4 . — 

 Authors abstract. 



Messrs. Hall and Sardeson classified the lower formation of 

 Iowa, Wisconsin and Minnesota, from studies of their own in 

 the field and of the fossils discovered, as follows : 



Silurian. 

 Saint Peter (= Chazy). 

 Shakopee (Upper Shakopee). 



Upper Cambrian. 

 Xew Richmond (Elevator B Sandstone). 

 Oneonta (Lower Shakopee) (= Low. Calcif. of N. Y.) 

 Jordan Sandstone (= Madison sort). 

 Saint Lawrence dolomites (= Mendota dolomites). 



Middle Cambrian. 

 Dresbach Sandstone. 



They found a Chazy fauna in the Saint Peter; in the Shakopee 

 a peculiar fauna which they were unable certainly to locate in 



