318 On the Tertiary Strata of Martha's Vineyard. 



Art. XII. — On the Tertiary Strata of the Island of Martha's Vineyard 

 in Massachusetts ; by Charles Lyell, Esq., V. P. G. S., &c* 



The most northern limit to which the tertiary strata bordering the At- 

 lantic have been traced in the United States, is in Massachusetts, in 

 Martha's Vineyard, lat. 41° 20' north, an island about twenty miles in 

 length from east to west, and about ten from north to south, and rising 

 to the height of between two and three hundred feet above the sea. 

 The tertiary strata of this island are, for the most part, deeply buried be- 

 neath a mass of drift, in which lie huge erratic blocks of granite and 

 other rocks, which appear to have come from the north, probably from 

 the mountains of New Hampshire. The tertiary strata consist of white 

 and green sands, a conglomerate, white, blue, yellow, and blood-red 

 clays, and black layers of lignite, all inclined at a high angle to the 

 northeast, and in some of their curves quite vertical. They are finely 

 exposed near Chilmark on the southwest side of the island, and in the 

 promontory of Gay Head at its southwestern extremity, where there is 

 a vertical section of more than two hundred feet in height. 



Attention was first called to this formation by Prof. Hitchcock in 

 1823, who appears to be the only American geologist who has examin- 

 ed them personally. He compared the beds at Gay Head to the plastic 

 and London clays of Alum Bay in the Isle of Wight, to which, lithologic- 

 ally, they bear a striking resemblance, consisting in both cases of vari- 

 ously and brightly colored clays and sands with lignite, all incoherent 

 and highly inclined. Various opinions, however, have been put forth as 

 to the relative age of the Martha's Vineyard strata, which were assign- 

 ed by Prof. Hitchcock, at a time when the tertiary formations of the 

 United States were less known, to the eocene^period, while Dr. Morton 

 supposed them to be in part only tertiary, and that they rested on green- 

 sand of the cretaceous period. 



The section at Gay Head is continuous for four fifths of a mile ; the 

 beds dip to the northeast generally at an angle of from thirty five to 

 fifty degrees, though in some places at seventy degrees. The clays 

 predominate over the sands. In one place Mr. Lyell found a great fold 

 in the beds, in which the same osseous conglomerate and associated 

 beds of white sand, on the whole fifty feet thick, were so bent as to have 

 twice a northeasterly, and once a southwesterly dip. In the yellowish 

 and dark brown clay near the uppermost part of the section at Gay 

 Head, and in the green-sand immediately resting upon it,f Mr Lyell 



* From the Proceedings of the London Geological Society, Vol. IV, No. 92. 

 t Nos. 5 and 6 of Prof. Hitchcock's section. 



