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REVIEWS. 157 
` The author states that even the largest dams are the work of a single 
constant repairs. Grass Lake dam, the largest one, perhaps, in North 
i ixty fe 
teen feet on the lower face. It has been supposed to kre an Tii be 
high intelligence that the beaver built its dam so as to ¢ eup s 
where the pressure of the water is the greatest, but the ehje ryen 
questions whether these curves are the result of accident or design. 
large streams. The dam generally curves down in those streams that 
discharge the largest volume of water, when also the dams are shorter 
and lower than those on the smaller brooks.” 
The great dam on Grass Lake, so fully described, “contains upwards 
of seven thousand cubic feet of solid materials.” This dam is also sup- 
plemented by an upper and a lower dam to break the force of the stream 
in freshets; the lower one setting the water back to the depth of twelve 
or fifteen Ionian in the great curve. Such structures are remarkable in- 
Stances of prevision and engineering skill, reminding us of the intelli- 
gence shown by the Agricultural Ant of Texas, which, according to 
Dr. Lincec cum, erects mounds on the “pavement” of its formicary in dry 
Weather, in anticipation of the rainy season! 
n excavating this artificial canal for transporting their wood by wat 
to their lodges, Bag evince the most intelligence and “a Riba i 
and extended process of reasoning,” though the work is simpler than 
ea a dam, ad like the latter, requires many years of continuous 
Like all close and patient observers of the habits of aaa the author 
believes that animals have a reason different only in degre m that of 
man. “When a beaver stands for a moment and looks a his work, 
evidently to see whether it is right, and whether anything else is needed, 
e shows himself capable of holding his thoughts before his beaver Pout 
in other wo rds, he is conscious of his own mental processes.” 
canal is not absolutely necessary to beavers any more than such a work ‘ 
mankind; but it comes to both alike, as the result of progress in 
miowiedge. A beaver canal could only be conceived by a lengthy and 
nM 
— ee abteddly , when the canal first came into use; and a time, conse- 
ntly, when it was entirely unknown.” The author hence argues a pro- 
T y knowledge, and hence improvement “from a lower toa higher 

