152 Tertiary. 



The encroachments of the sea upon the land, and the gain of the 

 land upon the sea, are discussed. The dunes or downs are described. 

 The Connecticut river is shown not to have excavated its own valley 

 entirely, though proofs are offered to show that it has cut out the last 

 ninety feet in depth, or all below the upper terrace which forms the 

 great valley of the Connecticut. The terraces found in the river val- 

 leys are described, and their origin accounted for on the supposition 

 that they were produced by the rivers when they run upon a higher 

 elevation than they do at present. The action of ice floods which con- 

 tinue to operate energetically in the Connecticut valley, and more pow- 

 ei'fully in the mountain torrents, are considered in relation to their 

 effects in modifying the surface and excavating the beds of rivers. It 

 is shown that the Connecticut river may have excavated its own valley 

 above Mount Tob}', in Sunderland, but that this is the only valley in 

 the State which is strictly a valley of denundation. 



He separated the Tertiary into the most recent Tertiary and the 

 plastic cla3^ The newest Tertiary is found in the Connecticut valle^^^ 

 and at Cambridge, Charleston, and other places. At Deerfield, it is 

 found more than sixty feet in thickness, and near Boston, from seventy 

 to one hundred and twent}^ feet. The plastic clay is found at Nan- 

 tucket and the southeastern part of the State. He considered the ex- 

 tensive beds of hydrate of iron in the limestone valle3"s of Berkshire 

 county, and. the claystones of the Connecticut valley as i.f Tertiary 

 age. The latter are concretions of carbonate of lime mixed with 

 cla}', such as that in which they are found, consisting of alumina and 

 fine sand, with occasional fine scales of mica. These concretions are 

 round, lenticular or oblate, and frequently joined together. The 

 diameter is from the thickness of a pigeon shot to two or more inches, 

 and the thickness is that of a single layer of clay, which rarely ex- 

 ceeds one half an inch. The Tertiary of the Connecticut valley, and 

 other interior places, he supposed to be of fresh water origin, and the 

 plastic clay a marine formation. The latter he separated into its 

 mineralogical characters, and described white pipe cla}-, blood red 

 clay, red and white clay, bluish gray plastic clay, white siliceous sand, 

 white micaceous sand, green sand, lignite, osseous conglomerate, and 

 other conglomerates and minerals. He noticed the organic remains, 

 and called attention to the fossil vegetables and animals. 



In the same 3'ear, Mr. Isaac Lea* described the Tertiary at Clai- 



* Contributions to Geology. 



