BASALTIC AND VOLCANIC ROCKS. 271 
six are found in the same formation in Europe. This 
deposite is also called marl^ and is extensively used 
in Virginia and other states for its fertilizing prop- 
erties. 
CHAPTER XXV. 
GEOLOGY OF THE UNITED STATES. 
BASALTIC AND VOLCANIC ROCKS. 
Basaltic and Volcanic Rocks. — Evidences of Volcanic Action in 
the Rocky Mountains. — Trap Rocks. — Bakewell's Definition 
of Basalt — Of Greenstone. — Localities of Greenstone Trap — 
In Massachusetts — New- Jersey — Columbia River — Nova 
Scotia. 
" The principal deficiencies in the geological for- 
mations of the United States," says Professor Sil- 
liman, are in the absence of active volcanoes, as 
Vi^ell as most of the members of the upper second- 
ary. However delightful active volcanoes, with 
their earthquakes and eruptions, may be to specu- 
lative geologists, the sober, unscientific population 
may well rest quite contented without them, satis- 
fied to barter the sublime and terrific for quiet and 
safety. Although the soils formed from decompo- 
sed lava are often fertile, and the vine flourishes, 
and the clusters smile most remarkably on the 
flanks and at the feet of the volcanic mountains of 
warm countries, these influences are too local to 
be of much importance to agriculture. 
" Within the United States proper, including the 
states and territories beyond the Mississippi and 
east of the Alleghany Mountains, there is not, so 
far as we know, a single active volcano, nor even 
an unequivocal crater of one that is dormant. Both 
north and south of our limits there are, on the Pa- 
