Correspondence—Mr. H. B. Woodward. 383 
America on its climate is only to express in another form the 
influence produced by the currents, for it is simply because of this 
extension that the Gulf Stream-does not reach the eastern shore of 
that part of America to which the comparison with Europe applies 
until it has passed through the refrigerator of the Polar Basin, and 
issued therefrom as the Polar, or Labrador current. Land not lofty, 
such as is most of that which forms the Polar extension of North 
America, has of itself no more refrigerating effect than sea which 
ameliorates climate only when warmed by equatorial currents, as the 
condition of the great Antarctic expanse of ocean sufficiently proves. 
I venture indeed to think that it has less so. Before Mr. Wallace 
can appeal to any ameliorating influence exerted on the climate of 
Europe by the Mediterranean (an influence to which the isothermals 
lend no countenance) as contrasted with America, he should show 
that the valley of the Mississippi was not submerged during the 
Glacial period. Some American geologists, as e.g. Dr. Newberry, 
insist that it was; and if so, not only would those conditions, on the 
absence of which Mr. Wallace relies, be present, but their infiuence 
be more considerable than any produced by the Mediterranean, 
because the water of the Gulf of Mexico, of which such sub- 
mergence would form an extension, is hotter than that of the 
Mediterranean. 
In testing Mr. Croll’s theory, however, we may confine ourselves 
to North America alone. Owing to the Gulf Stream leaving the 
eastern shore where these differences begin, and to the Labrador 
current hugging it down to that point, while the western shore is 
throughout washed by the warm water of the Pacific, the climate 
north of the 40th parallel presents on the eastern and western coasts 
contrasts similar to, though not quite so great as those which obtain 
between the West of Hurope and East of America. Now the 
glaciation on the eastern and western sides of America follows these 
existing differences of mean temperature just as it does in the case 
of Western Europe and Hastern America. Turn where we will, 
both in the northern and southern hemispheres, the climate of the 
Glacial period appears to have been an uniform diminution of mean 
temperatures as they now exist by virtue of geographical conditions 
and ocean currents ; and itis this which in my mind points so strongly 
to that period having resulted from a cosmical cause wholly uncon- 
nected with these conditions, that is to say, to a diminution in the 
heat-emitting power of the sun. SeaRuLes V. Woop, Jun. 
July 9th, 1880. 
P.S.—In my first letter I should have instead of ‘winter cold,” 
said mean temperature, as it is this which regulates glaciation. 
GLACIAL AND POST-GLACIAL. 
Srr,—In answer to the geological questions set by my friend Mr. 
Dalton in the July Number of this Magazine, I would remark that 
I know nothing in the brief notice of his “ Geology of Colchester” 
that can be gainsaid. The statement that the Bison, Klephas antiquus, 
