1894] Geology and Paleontology. 265 
the embouchures of the other rivers of the Coastal plain. It is repre- 
sented not only by the removal of fully one-half of the original vol- 
ume of the Lafayette formation, but by the degradation of an equal 
or greater volume of subjacent formations of Neocene, Eocene and 
Cretaceous age beneath. (Bull. Geol. Soc. Am., Vol. 5, 1894.) 
In a previous publication in the same periodical, Mr. Upham had 
concluded that the observed volume of the Plistocene glacial erosion 
and resulting drift had probably accumulated in from 10,000 to 20,000 
years. In the general conclusion of a short rather than a long period, 
Mr. R. S. Tarr agrees, but cannot accept Mr. Upham’s line of argu- 
ment, with our present knowledge of the rate of glacial erosion. Various 
complex factors make a time estimate of little value. Mr. Tarr bases 
his estimate on the following conditions. 
A glacier is supplied with material for erosive work in three ways: 
(1) it may carry along the loose material in its path; (2) it may rend 
rocks asunder whenever a place of entry is found ; (3) it may obtain 
material from the rock itself by scouring it with cutting tools already 
supplied. The erosive action of ice is to round, smooth and polish the 
surface over which it moves, lessening the possibility of obtaining a 
supply of cutting tools, so that as the period of ice occupancy lengthens 
the power of erosion diminishes. 
With these facts as a basis, a young glaciated region should be lit- 
tered with glacial drift, the products of disintegration. In a later 
stage the deposits would be composed of fresher rock fragments distrib- 
uted in greatest abundance near the periphery of the ice-sheet. Dur- 
ing old age the country would be free from deposits and the topography 
would consist of polished, rounded hills of glacial erosion. The first 
stage would be brief, the second longer, and the passage to extreme 
old age one of slow development. 
In accordance with these facts, Mr. Tarr concludes that the North 
American glaciated region is topographically young, or at most not far 
advanced into maturity. (Am. Geol., Vol. XII. 1893.) 
Geology of Marthas Vineyard.—Afier a personal investiga- 
tion of the geology of Marthas Vineyard, Mr. Hollick finds that the 
ridge of hills consisting of a superstructure of contorted clay strata 
capped and flanked to the north with till, is composed of material de- 
rived from cretaceous and post-cretaceous strata. He does not agree 
with Shaler that the dislocations and elevations of the strata are due 
to mountain-building forces, but that they can be accounted for by the 
‘Same theory that the author advanced for the modification of the strata 
