Review of Recent Geological Literature. 105 
form Long Island, Martha's Vineyard, Nantucket an<l a number of 
lesser islands, and an inner rid^e evident in cape Cod, the Eli%a))eth 
islands and several smaller islands. The eastern portion of this 
double coast frin>;e is separated from the western portion by a consid- 
erable gap, that which divides Martha's Vineyard from Block island 
and Lonji island. The cause of this break is not perfectly clear, but 
professor Shaler regards it as probably due, not to any failure of the 
glacial deposits to be formed in this space or in any considerable 
degree to their erosion, but rather to the fact that the floor on which 
they rest was originally lower in this part of the coast than elsewhere. 
This is indicated by the circumstance that from the western end of 
Martha's Vineyard there is a shoal that extends to Block islantl and 
thence to Long island. This shoal seems to be a continuation under 
water of the marginal drift formations which are so prominently 
exhibited on Long island and Martha's Vineyard. 
These drift deposits comprise (1) the ordinary ground moraine or 
till, left by the melting of an ice-sheet; (2) frontal moraine deposits, 
formed where the materials have been pushed before the glacier ; (3) 
kame deposits, where the materials have been brought to their position 
by the action of violent currents of water operating near the ice front ; 
and (4) terraces or plains, sloping southward from the belt of the 
frontal moraine and kames. 
The total amount of detrital material in the belt of moraines on the 
northwest part of Martha's Vineyard between Gay Head and Tashmu 
pond is greater than in any other deposit of this nature known to the 
author in New England. On an area ten miles in length and one and 
one-half miles in width the drift can not be on an average less than 
150 feet thick. Its highest elevation is Prospect hill, which rises about 
.300 feet above the sea. South of the hilly morainic belt on the eastern 
half of the island the surface passes rather suddenly into a plain of 
gravel and sand, which sirks from an elevation of 50 feet bordering the 
moraine to only about 10 feet a])ove the sea level at the southern shore 
of the island. 
Professor Shaler believes that the deposition of both the frontal 
moraine and the bordering plain took place at some depth below the 
level of the ocean, the relative bights of land and sea in that region 
having been so changed during the glacial period that even Prospect 
hill was submerged. This opinion, however leads to a startling con- 
clusion which is stated as follows: "The emergence of the drift 
deposits of this district from the sea must have taken place with sin- 
gular rapidity, for there is no sign of wear on the surface 
of the moraines or the lower-lying kames, such as would inev- 
itably have occurred if their surfaces had been exposed to the action 
of the waves for any length of time. Nothing save an exceedingly 
sudden uplift could have secured their escape in the process of eleva- 
tion ; theirextremoly delicate outlines could not endure the action of 
the sea for a single month." 
