456 



THE AZOIC SYSTEM AND ITS SUBDIYISIONS. 



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

 Jour. Sci., 187G, (3) XL, pp. G3, 64) : 



" Mr. Lesley goes outside of his field in his dosing 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 ILtmpshirc,' are, like 'the Laurontian Mountains of Canada/ older than 

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

 mountain systems of the north/ is Huronian. The observations by Mr. Prime 

 in Pennsylvania, above n)entioned, 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. Tlie writer has studied strati graphically .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 

 elates of the ridge lying northeast of Putland in Vermont, and of others west 

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

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

 West Kutland aljound in distinct Lower Silurian fo.ssils, referred to the Cluizy 

 by Billings, part of the Green Mountain slates and schists are un(piestionably 

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



Li 1878 Professor Dana remarks : 



"Professor Lesley stated in his letter* that the opinions which he h:id 

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

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

 stones anjong 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 Monntains, and also the White Mountains, and that the latter include 

 beds of Devonian age." (Am. Jour. Sch, 1878, (3) XV., p. 2()1.) 



This then is a virtual retraction by Professor Lesley of Ids statement 

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



Potsdam in ago. 



Professor Dana made the following statement as the result of 

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



■* A letter to Professor Pana, giving an account of tlio discovery by Ui; Prime 

 of Lower Silurian fossils associatc-d with mica slates in Kastern Pennsylvania. 



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

 {'.]) Ill, pp. 179-186, 250-256 ; IV., pp. i:!-b 362-370, 450-453 ; V., pp. 47-53, 

 8-1-91 ; VI., pp. 257-279 ; 1877, Xllh, pp. 332-347, 405-419 ; XIV., pp. 36-48, 

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

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

 XIX., pp. 50-54. 



