Review of Recent Geological Literature. 69 
River age, and not of Taconic age. Since Prof. Dana's field work was 
published, not only have the quartzyte and the limestone and shales 
which hediscussed been found to contain aTaconic fauna (01enellus,etc. ), 
but they have been found to pass into schists and gneisses. The orig- 
inal contention of Dr. Emmons as to the age of these metamorphic 
rocks has been abundantly verified. Again, Dr. G. H.Williams has also 
shown that the augitic, hornblendic and chrysolitic zones, supposed to 
have been produced by metamorphism in the sedimentary rocks, are 
true basic eruptions that invaded the Taconic strata probably prior to 
the commencement of the Lower Silurian, and have nothing to do with 
the original strata in age nor otherwise except to have modified them by 
contact. 
In treating of the Glacial period, the author confidently attributes 
the glacial and modified drift to the action of vast sheets of land ice, 
without important aid from marine submergence, icebergs, and floes. 
Previous to the ice accumulation the altitude of the glaciated countries 
is thought to have been generally somewhat higher, or at least not 
lower, in relation to the sea level, than now. While the lands were ice- 
covered they are shown to have been somewhat depressed, allowing the 
formation of marine shore-lines and fossiliferous sea deposits upon the 
glacial drift after the retreat of the ice; but the submergence thus indi- 
cated nowhere exceeds oOO or 600 feet, as in the St. Lawrence valley and 
in Scandinavia. For some parts of Great Britain a probable submer- 
gence of about 500 feet is claimed, though the highest well defined 
marine terraces and beaches cited are only about 100 feet above 
the sea. The mass of stratified clay with marine shells enclosed in the 
till at the hight of 524 feet at Chapelhall in Lanarkshire, and the 
shell-bearing drift sand and gravel at greater hights, up to 1200 and 
1350 feet, respectively, in Cheshire and on Moel Tryfaen in northern 
Wales, are regarded as more probably due to glacial transportation from 
the bed of the Irish sea than to the presence of the ocean at those 
altitudes. 
The lower and upper deposits of boulder clay or till, which are gen- 
erally distinguishable over the greater part of the drift-bearing area of 
Europe, are ascribed to successive glacial epochs, divided by an inter- 
glacial time of general disappearance of the ice-sheets and prevalence 
of a mild climate, as known in some localities by the preservation of 
traces of the interglacial fauna and flora. But in view of the recent 
discussions and diverse interpretations of the evidences of such changes 
in America, the author leaves it an open question whether the Ice age 
shall be considered so distinctly twofold or multifold as the upholders 
of the astronomic theory of the causes of the glacial climate have 
taught. His reference of the outermost and next succeeding moraines 
of southern New England and Long Islond to "distinct and perhaps 
widely separated epochs in the Ice age" differs from the present views 
of most or probably all American glacialists. Not only these moraines, 
but also others described by Tarr and Hitchcock farther north in New 
England, the fifteen or more approximately parallel moraines traced by 
