8 THE CANADIAN NATURALIST. [March 



eastern Massachusetts, which were described by the late Dr. 

 Hitchcock as enclosed in the great gneissic and hornblendic form- 

 ation stretching through that portion of the state. These lime- 

 stones, which are met with at various points from Bolton by 

 Chelmsford on to Newburyport, present a close mineralogical 

 resemblance to those of the Adirondacks and Laurentides, and 

 also to those of the Highlands of New York and New Jersey, 

 a resemblance which extends to the gneissic rocks which in 

 these various regions accompany the crystalline limestones. I, 

 at that time, accepted without examination the view maintained 

 by Mather and H. D. Rogers, that these limestones in southern 

 New York and New Jersey were altered Silurian strata, although 

 mineralogically identical with those farther north of undoubted 

 Laurentian age. Led by this conclusion to attach comparatively 

 little importance to mineralogical and hthological resemblances, 

 and guided by other considerations given in the paper just referred 

 to, I then suggested that the crystalline limestones and their 

 accompanying rocks in north-eastern i\J assachusetts might probably 

 be of Devonian age. The subsequent investigations of Hall, 

 Logan and Cooke in the Highlands of New l^'ork and New Jersey 

 have however left no doubt that these supposed altered Silurian 

 rocks are really of Laurentian age, and led me to suspect that the 

 same might be the case with those of eastern Massachusetts. 

 This view, which was shared by Prof. James Hall, I ventured to 

 put forward at the meeting of the American Association for the 

 Advancement of Science at Salem in August, 1869, when I 

 showed that it was probable, not only on Hthological grounds, but 

 from the fact that the Laurentian rocks appear to the southward 

 of the great palaeozoic basin in New Brunswick and Newfound- 

 land^ which are geologically but a north-eastein prolongation of New 

 England, and moreover from the outcropping of the lowest Silu- 

 rian strata at Braintree, near Boston. A few days later I visited 

 Newburyport, and in company with Dr. Henry C- Perkins of 

 that place, had, for the first time, an opportunity of observing 

 the gneisses and limestones in question. Their aspect confirmed 

 my suspicion of their Laurentian age, and led me to suggest to 

 him the propriety of searching for Eozoon Canadense in the 

 limestone which there occurs mingled with serpentine. Speci- 

 mens of it were thereupon placed in the hands of Mr. Bicknell of 

 Salem, well known as a skilled microscopist, and shortly after it 

 was announced by Dr. Perkins that Mr. Bicknell had discovered 



