312 ANNUAL OF SCIENTIFIC DISCOVERT. 



ON THE GEOLOGY OF THE CENTRAL PALEOZOIC BASIN, OR AREA 



OF MIDDLE NORTH AMERICA. 



In a paper communicated by Dr. I. J. Bigsby to the Quarterly Journal of 

 the Geological Society of London, Vol. xiv. Part 4. No. 50, the author deduces 

 the following conclusions respecting the geology of the central palaeozoic 

 basin or area of middle North America : 



1. That, whatever may be the case elsewhere, the Silurian and Devonian 

 systems of New York are parts of one connected and harmonious period, - 

 the product of successive and varying Neptunian agencies, operating in 

 waters which deepened westward from the Atlantic, and southwards from 

 the Laurentine chain on the north. 



2. That from the Catskill group (Old Red Sandstone) downwards through 

 the whole series, to the Potsdam Sandstone, there is perfect and close- cou- 

 formability, and no such unwonted change in fossil life as to constitute a 

 systematic break, except at one place the Oriskany Sandstone, the base of 

 the Devonian in New York, there being no break of like importance at 

 the Oneida conglomerate period, contrary to an opinion towards which able 

 geologists are now inclining, an opinion which leads them to consider the 

 break at the Oneida conglomerate as systematic. 



3. All the palaeozoic groups of New York slowly pass one into the other 

 by gradation of mineral and organic characters, with easily explained 

 exceptions. 



4. The palaeozoic strata of New York are comparatively thin. They seem 

 to have lost in thickness what they.have gained in extension. 



rocks, in opposition to the view of the older geologists, who supposed them to have 

 been built up by the accumulation of successive eruptions, although supported by 

 Humboldt, Vou Buch, and Elie de Beaumont, has been from the first opposed by 

 Cordier, Constant Prevost, Scrope, and Lyell. (See Scrope, Geol. Journal, vol. xii. p. 

 326, and vol. xv. p. 500; also Lyell, Pkilos. Trans, part 2, vol. cxlviii. p. 703, for 1858.) 

 In these will, we think, be found a thorough refutation of the elevation hypothecs, 

 and a vindication of the ancient theory. 



This notion of paroxysmal upheaval once admitted for volcanoes, was next ap- 

 plied to mountains, which, like the Alps and Pyrenees, are composed of neptuniaii 

 strata. Against this view, however, we find De Muntlo.-ier. in 1S32, maintaining 

 that such mountains are to be regarded only as the remnants of former continent.-, 

 which have been cut away by denudation ; and that the inversions and disturbances 

 often met with in the structure of mountains are to be regarded only as local acci- 

 dents. Bui. Soc. Geol., (l)vol. ii. p. 438, vol. iii. p. 215. 



Similar views were developed by Prof. Hall, in his address before the American 

 Association for the Advancement of Science, at Montreal, in August 1857. This 

 address has not been published, but they are reproduced in the first volume of his 

 Report on the Geology of Iowa, p. 41. He there insists upon the conditions which, in 

 the ancient seas, gave rise to great accumulations of sediment along certain lines, 

 and asserts that to this great thickness of strata, whether horizontal or inclined, we 

 are to ascribe the mountainous features of North Eastern America as compared 

 with the Mississippi valley. Mountain heights are due to original depositions and 

 subsequent continental elevation, and not to local upheaval or foldings, which, on 

 the contrary, give rise to lines of weakness, and favor erosion, so that the lower 

 rocks become exposed in anticlinal valleys, while the intermediate mountains are 

 found to be capped with newer strata. 



In like manner, J. P. Lesley asserts that "mountains are but fragments of the up- 

 per layers of the earth's crust," lying in synclinals, and preserved from the general 

 denudation and translation. Iron Manufacturer's Guide.. 1859, p. 53. 



