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Rh To this Mr. Hopkins sees no a priori objection; but he does not feel disposed to attach much weight to it, because it is "a mere hypothesis framed to account for a single and limited class of facts, and unsupported by the testimony of any other class of allied, but independent phenomena."

I must refer to Mr. Hopkins' paper for his objections to this suggestion, which certainly appear to "render the theory utterly inapplicable to the explanation of the changes of temperature at the more recent geological epochs." (l. c. p. 62.)

This cause, which has been advocated by Sir C. Lyell with so much ability, would no doubt have the effect attributed to it, but it seems scarcely applicable to the present difficulty, because the geography of Western Europe must have been nearly the same during the period under consideration, as it is at present. The existence of a continent north of Scandinavia and Scotland, might indeed go far towards accounting for the phenomena; but to this suggestion we must make the same answer as to the first.

The possibility of such a change has indeed been denied by many astronomers. My father, on the contrary, in a letter to Sir C. Lyell, has maintained that it would necessarily follow from upheavals and depressions of the earth's surface, if only they were of sufficient magnitude. This suggestion, however, like the preceding, involves immense geographical changes, and would therefore necessarily have required an enormous lapse of time.

5thly. Mr. Hopkins, in the paper to which I have already alluded, inclines to find another solution of the difficulty in the supposition that the Gulf Stream did not at this period warm the shores of Europe "A depression of 2000 feet would," he says, convert the Mississippi into a great arm of the sea, of which the present Gulf of Mexico would form the southern extremity, and which would communicate at its northern extremity with the waters occupying the. . . . . . great valley now occupied by the chain of lakes." In this case the Gulf Stream would no longer be deflected by the American coast, but would pass directly up this channel into the Arctic Sea; and as every great ocean current must have its counter current, it is probable that there would be a flow of