-Review of Recent Geological Literature. 191 
submerged Tertiary formation several hundreds of miles in length, con- 
stituting, very likely, the solid foundation of the banks. The banks, 
therefore, with their complex of valleys, can be classed with the ex- 
tended submerged Hudson channel and other submarine valleys off the 
California coast, and with the fiords of all our northern coasts, as evi- 
dences of a great epeirogenic uplift of the northern part of the North 
American continent, preceding and producing the Ice age. 
The Conditions of Erosion beneath deep glaciers, based upon a study 
of the Boulder Train from Iron Hill, Cumberland, E. I. By N. S. 
Shaler. Bulletin of the Museum of Comparative Zoology at Harvard 
College, vol. xvi, pp. 185-225, with a map and four plates; Jan., 1893. 
The rock of Iron hill is a peridotite, a phase of olivine gabbro, yielding 
25 to 45 per cent, of metallic iron. Its peculiar and conspicuous ap- 
pearance, unlike that of any other rock in New England or even in the 
United States, makes it possible to observe very accurately the extent 
of its glacial transportation. The outcrop, which is believed to be a 
volcanic neck or dike, measures about 1,200 by 500 feet, and rises 60 
feet above the adjoining somewhat level, drift-covered country. At this 
source the width of the boulder train is about 700 feet, but in its extent 
thence to the south it gradually widens to four miles in the vicinity of 
Providence, about fifteen miles from Iron hill; and in the next twenty- 
five miles to Newport and the mouth of Narragansett bay it expands to 
a width of nearly eight miles. Onward it fans out more rapidly, so 
that its east side touches the west end of Martha's Vineyard. Close to 
Iron hill the largest boulders are four to five feet in diameter, but 
thence they diminish in size to only one foot near Providence, and to 
five inches on Martha's Vineyard, where only three fragments have 
been found. The boulders are embedded in the till, being there inter- 
mingled with others from the various rock formations both north and 
south of Iron hill. The widening or fanning out of the boulder train 
Prof. Shaier ascribes to currents of subglacial water, working the drift 
over perhaps several times before it was finally deposited by the ice- 
sheet as till. From the volume of its contribution to the drift, and 
from studies of the glaciated rock surface, Iron hill appears to have 
been glacially eroded at the surprisingly rapid rate of six inches, or 
perhaps even a foot or more, for each mile of the ice advance; but 
about four fifths of the eroded rock was borne away as sand and fine 
flour, only one-fifth being boulders, whose scars on the surface of the 
outcrop show where they were plucked away. A very short time, geo- 
logically speaking, would suffice for the glaciation of New England at 
this rate, which seems to imply the removal of at least an inch of this 
very hard rock yearly. Since the preservation of the grand features of 
the preglacial contour upon the drift-bearing region of the United 
States and Canada is usually very evident, probably the average glacial 
erosion is rarely so much as 100 feet, which would require only 1.200 
years. Such brevity of the ice wear, however, seems to Prof. Shaler 
consistent with a much longer duration of the Glacial period, accord- 
ing to his most extraordinary and ingenious hypothesis that the pres- 
