308 Recent Literature. [April, 
of denudation and deposition (twenty-eight million years) is nearly 
midway between these, and it is, at all events, satisfactory that the 
various measures result in figures of the same order of magnitude, 
which is all one can expect in so difficult and exceedingly specu- 
lative a subject. 
“ The only value of such estimates is to define our notions of 
Mr. Wallace not only discards some of the exaggerated hypothe- 
ses of well-nigh limitless geological periods, but also the far-fetched 
ideas of intercontinental bridges and temporary islands, which so 
excellent a biologist as Professor Huxley is fond of invoking even 
up to the present year, and of the hypothetical Lemuria of Haeckel, 
and has fully adopted the well-grounded view of the permanence of 
the present continents and ocean basins. To American geologists 
Le . 
the origin of the North American continent from the Laurentian 
the European-Asiatic continent there may have been a slight 
interchange of forms. Simultaneous with the growth of the 
