450 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



Professor Dana, in a review of Professor Lesley's remarks, says (Am. 

 Jour. ScL, 187G, (3) XL, pp. 03, G4) : — 



" Mr. Lesley goes outside of his field in his closing remarks, and states — 

 what is sustained as yet by no adequate stratigraphical evidence — that the 

 'Green Mountain system of Vermont 'and the 'White Mountain system of 

 New Hampshire,' are, like ' the Laurentian Mountains of Canada,' older than 

 the Potsdam ; and that the Green Mountain system, one of these ' three great 

 mountain systems of the north,' is Huronian. The observations by Mr. Prune 

 in Pennsylvania, above mentioned, and the parallel facts in the Green Moun- 

 tain system to which he draws attention, all point as regards the Green Moun- 

 tains in the opposite direction. The writer has studied stratigraphically the 

 Green Mountain region from Connecticut to Vermont, and has found that the 

 hydro-mica and chloritic hydro-mica slates associated with the limonite beds of 

 Berkshire are of the same formation with the hydro-mica, chloritic, and mica- 

 ceous slates of Graylock and the Taconic range ; and with the hydro-mica 

 slates of the ridge lying northeast of Rutland in Vermont, and of others west 

 and north of Rutland ; and with the staurolitic schists of the limonite region 

 of Salisbury, Connecticut. Since the limestones associated with the slates of 

 West Rutland abound in distinct Lower Silurian fossils, referred to the Chazy 

 by Billings, part of the Green Mountain slates and schists are unquestionably 

 Lower Silurian. What is the age of the rest is not yet positively known." 



In 1878 Professor Daua remarks : — 



"Professor Lesley stated in his letter* that the opinions which he hod 

 derived, from the observations of others, more than thirty years since with 

 regard to New England geology, he now (since the discovery of fossils in lime- 

 stones among the metamorphic rocks of Vermont, of Bernardston and Littleton 

 in the Connecticut Valley, and of Eastern Pennsylvania) regards as greatly 

 strengthened in probability — namely : That Paleozoic rocks make up the 

 Green Mountains, and also the White Mountains, and that the latter include 

 beds of Devonian age." (Am. Jour. Sci., 1878, (3) XV., p. 26L) 



This theu is a virtual retraction by Professor Lesley of his statement 

 in 1875 (given before), that the Green and Wliite Mountains were pre- 

 Potsdam in age. 



Professor Dana made the following statement as the result of 

 an extended series of observations f by himself and Kev. Augustus 



* A letter to Professor Dana, giving an account of the discovery by Mr. Prime 

 of Lower Silurian fossils associated with mica slates in Eastern Pennsylvania. 



t For Professor Dana's various papers on this subject, see Am. Jour. Sci., 1872, 

 (3) III., pp. 179-186, 250-256 ; IV., pp. 133, 362-370, 450-453 ; V., pp. 47-53, 

 84-91 ; VL, pp. 257-279 ; 1877, XIII., pp. 332-347, 405-419 ; XIV., pp. 36-48, 

 132-140, 202-207, 257-264 ; 1879, XVII., pp. 375-388 ; XVIII., 61-64 ; 1880, 

 XIX., pp. 191-200. See also Dwight, Am. Jour. Sci., XVII., pp. 389-392 ; 1880, 

 XIX., pp. 50-54. 



