146 
land, to accept Ramsay’s conjecture that there were two 
glacial epochs, — one before, and the other after the drift. 
The following year, 1851, he visited the White Moun- 
tains, and studied the effect of one of those tremendous 
stone-slides which have played so important a part in the 
reduction to its present level of the central massif of New 
Hampshire, upon the face of the rock in situ over which it 
passed. Seeing no glacial markings whatever, he concluded 
that any aqueous theory of diluvial scratches must be insuf- 
ficient. He had evidently come to feel the difference 
between the weight of a stone-slide, whether in or out of 
water, and the weight of a glacier or iceberg. 
Finally, in 1857, appeared his contribution to the quarto 
publications of the Smithsonian Institution, called Illustra- 
tions of Surface Geology, in which he sums up his knowl- 
edge of the Drift. In the first part he compares the terraces 
of the Connecticut Valley with those of other regions. In 
the second part he discusses the modes and consequences of 
river erosion; and in the third part he gives the results of 
his previous five years’ field work, devoted to the study of 
glacial strie and moraines in the valleys of Massachusetts 
and Vermont. These moraines, he says, seem to him, like 
the Swiss moraines, to have been modified and obscured 
subsequent to their creation by another agency, which he 
does not distinctly call that of the Drift, but, as he ex- 
presses it, “by the long-continued presence and the action of 
water, as the surface emerged from the deep.” Even at this 
late date, he had no distinct hypothesis to offer. He declared 
that he agreed more nearly with Mr. Redfield’s views than 
any others. He thought “that the phenomena of boulders 
and drift should be attributed to mixed causes, and that the 
_ theories which refer these phenoniena to the several agencies 
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