32 The American Geologist. .lamiHry, ik!«- 
thorc might have Vtocn, as professor Dana has sngjjpstefl, ' a siib- 
sidenci' about 1(1 or 15 feet lK'lf)\v \\\v present level, it appears 
that evon this slijjht amount cannot he allowed until a series of 
mcasTiremiMits in different localities ^^ives closely correspondinji; 
values for the extrenn' marine limits. 
Miirtliii s I liK ijii ril . 
On Martha's Vineyard, where I had the advantage of J*rof. N. 
S. ShaUu's guidance. 1 could only confirm his observation that 
no raised beaches of any kind rtcic to l)c seen. Where the termi- 
nal moraine touches the Hats of Tertiary clays, the toj)ographical 
features are sometimes at a distance terrace-like, but no true 
marine terraces either cut or built could be observe<l. So com- 
plete indeed is the preservation of the topography from marine 
e,rosion that j)rofessor Shaler. who lias thoroughly, investigated 
the island, has come to tlu' conclusion, that if this tract has been 
submerged it must have Imh'u uplifted (|uite suddenly. Hut it 
seems unntH-.essary to make use of this exi)lanation : for while I 
have not seen many of the kamcs in this locality, 1 should 
imagine that it would be easier to account for their ridge-like, 
winding shape, if we assume that they, like the ordinary osars, 
originated between walls of land-ice or possibly in some cases of 
river-ice and snow. If they had been deposited in the sea. it 
would appear that the shape should have Ijeen more like a delta 
or a built terrace. As to the submerged valleys on ihc southern 
side of the island, these might also l)e most readily explained b}" 
supra -marine erosion of glacial rivers: for if the}' were formed 
l»elow the sea-level, by bottom-currents, coming from the months 
of sub-glacial rivers, we might expect them to )>c l)roadcst and 
deepest at th(ur beginning, whereas on the contrary they regu- 
larly increase in size as they depart from the terminal moraine. 
Moreover it seems scarcely i)robabIc that such curi'cnts could 
have kept together for more than live miles, and it is specially 
ditticult to account for Ihc fact that all the small tril»utaries come 
in at great angles. Furthermore. 1 may remark that all the 
glacial rivers that T have oltscrvc(l in Sj)itzlicrgcn pour out their 
muddy waters as a thin layer on the surface of the soa. cv('n i4i 
the interior of the fjords, where the sea-water is probably much 
less salt than on the open glacial coast of Marthas Vineyard. 
* " On Southern New England during the melting of the great 
glacier." .\in. Jour. Sci.. iii.. vol. \.. Dec, IS75. j). 4.'M. 
