Revieiv of Recent Geological Literature. 113 
The same consideration may also explain much of the difference in 
these respects between the outer part of the drift along all the glaciated 
area of the United States and that lying farther inside the glacial 
boundar)', as within the terminal moraines of the upper Mississippi 
region. 
In all the pebble-drift sections of Nantucket, Prof. Shaler finds plen- 
tiful subangular rock fragments, with the fractured edges only slightly 
worn, some of which closely resemble palfeolithic implements. He 
regards these as indicative of a long interval between two ice incur- 
sions, the earlier bringing boulders and pebbles in which joints and 
cracks were subsequently developed, and the later ice-sheet breaking 
these masses and strewing their subangular parts in its drift. Another 
explanation, however, seems to be afforded by the probable occur- 
rence of such joints and cracks in preglacial gravel or shingle and in 
masses left during the disintegration of ledges, so that there may have 
been only a single glacial advance to Nantucket. 
The richly fossiliferous post-Pliocene beds in the lower part of the 
section of Sankaty Head, on the east shore of the island, were first 
examined by Messrs. Desor and Cabot. Afterward more full collec- 
tions, and the discrimination of two shell-beds separated by a Serpula 
layer, were made by Messrs. S. H. Scudder and Richard Rathbun, 
the species being determined by Prof. A. E. Verrill, whose list and 
notes are here. copied in full. The lower shell-bed contains about 
thirty-five species which make xip a faunal group of distinctly southern 
character, all of them being now found living on the southern shores 
of New England, but several having their northern limit at Cape Cod. 
The species of Serpula is also of southern range, reaching from this 
limit to North Carolina. The upper shell-bed has about the same 
number Of species as the lower, but only thirteen are common to both. 
The new species brought in by the upper bed are mostly of northern 
range ; though all of these are found as far south as Massachusetts 
bay, several of them have their southern limit here or on the south 
coast of New England. The differences, however, according to Prof. 
Verrill, may not be due to any general climatic change in the tem- 
perature of water or of air, but rather to geographic modifications of 
the low shores and shallow sea in this vicinity, by which this place, 
for a time sheltered, became later exposed to cold marine currents and 
the surf of northeast storms. The only similar preglacial or intergla- 
cial fossiliferous section along the whole drift-bearing portion of our 
Atlantic coast is on the shore of Gardiner's island, about sixty miles 
distant to the west. 
Professor Shaler believes that during the form;ition of the terminal 
moraine on Nantucket this area was submerged so that its hill tops 
were some 200 feet below the level of the sea. This he thinks to be 
shown t)y the boulders strown over the morainic kame deposits, which 
he supposes to have been dropped from icebergs, and by the contour of 
these deposits, which are not only destitute of lines of shore erosion 
