W. Hopkins on Changes of Climate. 339 
to the present northern shores of the American continent, higher 
than that of Iceland, and more nearly resembling that of some 
parts of our own island. 
to learn whether any distinct indications had been observed of 
this climatal condition of the region in question, and recollecting 
tohave heard my friend Prof. E. Forbes make incidental men- 
sions, to ascertain the precise locality in which these remains 
had been found, and the period to which they belonged. A few 
days ago I received his reply, stating that these plants might be- 
long to the pleistocene period, and that the locality in which they 
been found was precisely that above spoken of, along the 
flanks of the Rocky Mountains and between them and Hudsou’s 
Y; as the region of which the temperature would probably be 
80 much affected by the warm current from the Gulf of Mexico. 
Teannot but regard these remains as strongly confirmative of the 
view which I have now ventured to propound. ~ 
Bat how, it may be asked, could such a warm current be con- 
‘istent with the glacial phenomena of the North American conti- 
hent? I have already intimated the reply to this question. ‘The 
exact period of these phenomena might be either anterior or pos- 
leriot to that during which the Gulf-stream made its way to the 
Arctic Sea. Suppose the superficial configuration of that conti- 
nent previous to its submergence to have been similar to its pres- 
*nt configuration. A gradual subsidence might convert the nor- 
‘ern portion of the continent into an arctic sea long before a 
land Were only approximately and not accurately similar, or if 
the submergence were more rapid in the north than in the south, 
the boundary of the extended Arctic Ocean might pass sgt to 
Valley of the Mississippi, before the Gulf of Mexico extended its 
Waters much to the north of its present boundary. In like man- 
het, similar conditions might obtain during the subsequent emer- 
8etce of the land. Minor hypotheses of this kind, entirely sub- 
lary to the general hypothesis with which they are associated, 
Must be considered as always admissible, and can only be tested 
Y observed phenomena. One remark, however, should here be 
: The periods of greatest cold in America and western 
