ee es ee ee 
* 
AMERICAN 
[SECOND SERIES.] 
a —Comparison of Experiments on America and Foreign 
Building Stones to determine their relative strength and du- « — 
= rability ; by Prof. Watrer R. Jounson, of Washington, D. Cue 
¥4; ioe Nave in the United Siiites but few ancient banda 
of which can furnish conclusive proofs of the dure ; 
sir materials, and as but few of the materials which 
4 ? 
American rocks as have been made, but also between fake: Pas 
such foreign materials as have been tested by the most careful ~ 
enters, and have besides ‘undergone the more decisive ; 
proofs. of many centuries of use in public edifices and’ monu- 
As nature has in many situations exposed t x us 
ials to the direct action of all the causes which can wor 
xtends, but during the Boplogiea| ages which run 
urably beyond all human history. Tho 
denuding, disintegrating and decomposing | 
erived from sweeping currents of water, from me 
Siieres: of | temperature, or from vegeta 
s, Vol. XI, No. 31.—Jan,, 1851. a 
