242 GEOGNOSY OF THE APPALACHIANS. [XIII. 



ries, and were followed by its calcareous division, which seems 

 to have included the limestones of the Trenton group ; all of 

 these rocks being supposed to dip to the westward, and away 

 from the central axis of the Green Mountains. Eaton does not 

 appear to have studied the White Mountains, nor to have con- 

 sidered their geological relations. They were, however, clearly 

 distinguished from the former by Charles T. Jackson in 1844, 

 when, in his report on the geology of New Hampshire, he de- 

 scribed the White Mountains as an axis of primary granite, 

 gneiss, and mica-schist, overlaid successively, both to the east 

 and west, by what were designated by him Cambrian and Silu- 

 rian rocks ; these names having, since the time of Eaton's pub- 

 lication, been introduced by English geologists. While these 

 overlying rocks in Maine were unaltered, he conceived that the 

 corresponding strata in Vermont, on the western side of the 

 granitic axis, had been changed by the action of intrusive ser- 

 pentines and intrusive quartzites, which had altered the Cam- 

 brian into the Green Mountain gneiss, and converted a portion 

 of the fossiliferous Silurian limestones of the Champlain valley 

 into white marbles.* Jackson did not institute any compari- 

 son between the rocks of the White Mountains and those of 

 the Adirondacks; but the Messrs. Rogers in the same year, 

 1844, published an essay on the geological age of the White 

 Mountains, in which, while endeavoring to show their Silurian 

 age, they speak of them as having been hitherto regarded as 

 consisting exclusively of various modifications of granitic and 

 gneissoid rocks, and as belonging "to the so-called primary 

 periods of geologic time." t They, however, considered that 

 these rocks had rather the aspect of altered palaeozoic strata, and 

 suggested that they might be, in part, at least, of the age of the 

 Clinton division of the New York system ; a view which was 

 supported by the presence of what were at the time regarded 

 by the Messrs. Rogers as organic remains. Subsequently, in 

 1847,J they announced that they no longer considered these to 



* Geology of New Hampshire, 160-162. 

 t Amer. Jour. Sci. (2), I. 411. 



* Ibid. (2), V. 116. 



