REPORT ON THE GEOLOGY OF NORTH AMERICA. 19 



describes them under the name of the most recent tertiary, 

 which I have stated to be my own view. But he makes a di- 

 stinction between these and other similar beds in Martha's 

 Vineyard and elsewhere, which he calls plastic clay. The first, 

 he says, are horizontal layers of white siliceous sand and blue 

 plastic clay, almost entirely destitute of any organic remains. 

 These beds constitute most of the level and elevated terraces 

 along the valley of this and most of the other rivers of New 

 England; the height of the plains above the water is from 

 fifty to one hundred feet. Along the Connecticut, in some 

 places, the clay beds alone compose the clifi", and are from forty 

 to more than seventy feet thick. They repose beneath fifteen 

 or twenty feet of diluvial matter. Their position, and all their 

 features, here and everywhere else, indicate a general uplift of 

 the strata along the whole line of the primary boundary when 

 that boundary formed the coast, and a consequent emergence of 

 these beds from about the water level, where they seem to have 

 grown as marshy deltas, accumulated along the ancient mouths 

 .of the rivers. On this supposition, the mouths of the Atlantic 

 rivers were at the points where they now form their falls, and 

 break through the boundary of the older rocks ; and it is singular 

 enough that all the conspicuous deposits of these clays, imbed- 

 ding the trunks of trees and lignite, are just opposite, or near to, 

 the same points. At Gay's Head, on the coast of Martha's Vine- 

 yard, are alternating sands and clays, which I refer to this for- 

 mation, rising in the cliff to a height of between 150 and 200 

 feet. The clays contain a bed of lignite, which is, in some 

 places, five feet thick. It alternates with the clays, especially 

 -the blue, and is often intimately mixed with them, forming a 

 comminuted dark mass, resembling peat. Woody fibre is often 

 distinguishable in it, and the whole has the appearance of a 

 deposit of peat, through which logs are interspersed. The prin- 

 . cipal beds lie not far from the middle of the cliff, and have a dip 

 of from 40° to 50° north. In this lignite bed are found impres- 

 . sions of dicotyledonous leaves, apparently Ulmus, Salix, &c., 

 trees at present growing in the country. Associated with these 

 beds of clay, however, occur several variations of sand; and what 

 at first seems startling enough, one bed described as a green sand, 

 containing remains of Crabs, casts of shells, Alcyonites, &c., 

 evidently referrible to the cretaceous formationof New Jersey, and 

 also interstratified with the same osseous conglomerate, from 

 which were procured the teeth of a Crocodile and several bones, 

 some of them very large, being nine inches thick, and as much 

 in length. The worn and mutilated state of these remains, and 

 the mixture in which they are found, prove forcibly that the bed 



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