magnesia more than the older ones; but ‘since ‘all of them contain 
enough of these and other mineral ingredients for the wants of plants, 
an excess of some of them cannot sensibly affect vegetation. The 
mineral composition of this ‘¢.one soil,” by a mean of numerous anal- 
yses, the author states to be, in 100 parts, 89.25 of sand, or silicates, 
and 0.85 salts of lime. 
Thus far we agree essentially with the author. But there are some 
other facts, which lead us to question whether the statement of this first 
principle does not require modification. It cannot be doubted, in the first 
place, that some silicates, (varieties of feldspar, for instance,) are decom- 
posed, both by atmospheric agencies and by growing plants, with much 
more facility than others; and consequently vegetation obtains from some 
soils the alkali, lime, and silica, which it needs, more easily than from 
others. In the second place, where an extensive region is underlaid 
by limestone, a large per cent. of the soil (from 5 to 30 in some parts 
of Europe) consists of carbonate of lime, and this is usually more easily 
decomposed than silicates, and will more readily supply carbonic acid. 
' The’second principle is, that “rocks do not affect the vegetation 
which covers them.” Here again, while we agree with the author that 
this principle is generally true, far more generally so than is commonly 
admitted, we would suggest to him whether there are not exceptions to 
it, too important to be overlooked in stating it. A similar difficulty we 
feel in respect to his third principle, that “‘rocks have not formed the 
ov wie ase ie them.” And we can Ses goer perhaps, state our 
f them in the same paragraph. 
Tt inte that what has been : éalted diluvial action, a9 weibud alluvial 
agency, has mixed up the detritus of different formations, and spread 
the soil derived from one rock over others. But the great mass of the 
soil has in very few cases been removed more than a few miles, 
although ~ single bowlders have been carried hundreds of miles. 
Hence, when we have gone a few miles from the borders of a forma. 
tion, the soil is made up almost entirely of its pulverized 
temoved, it may be a short distance, but still derived from precisely 
the same rock as that beneath it. Again, limited formations are 
soinetimes so situated that little if any foreign detritus has been left 
upon them, as for instance, the trap ranges along Connecticut river. 
From both these causes it happens, that over a large part of our coun- 
tty, each rock formation of much extent, does present a peculiar soil, 
which the geologist easily recognizes as derived from the subjacent 
rock. That above wee and gneiss, for instance, is light colored and 
v: that- ys and mica —. sade and relagnys 
PeeRE  neRY ret ora tha x statement, that rocks have 
