122 
AMERICAN GEOLOGY. 
tain chains. In the old world the direction is nearly east and 
west, and in the new 3 north and south; both continents are there¬ 
fore prolonged in the directi on of these mountain chains. The de¬ 
scription of the subordinate mountain chains will be furnished in a 
subsequent part of this work. The geological column is designed 
to show the relation of the systems of rocks to each other. The 
sediments or hydroplastic rocks are represented as reposing upon 
each, according to their age; and though the pyrocrystalline 
are represented as lying also one above the other, this is by no 
means the constant order of arrangement. Fig. 1 represents 
granites of different ages, penetrated by a volcanic funnel or 
tube, terminating in a crater. Figs. 3 and 4 a trap dyke and 
vein intersecting the laminated pyrocrystalline rocks, which 
consist of masses of gneiss, mica slate, hornblende, and talcose 
slate, upon which the oldest of the sediments, the Taconic sys¬ 
tem, reposes. At different places, however, the several systems 
of sediments are found reposing directly upon the primary and 
crystalline rocks. Thus the permian system in North Carolina; 
the new red of the Connecticut valley rest upon the pyrocrys¬ 
talline rocks, proving that the places where those rocks are 
spread out and deposited, were subserial until these geological 
periods. The relative lengths of the geological periods are 
approximately represented in the column. It shows to the eye 
that the paleozoic periods were immensely longer than the 
messozoic and kainozoic. These periods are the great triads 
of geologic history. The paleozoic, is the period remarkable 
for its duration; the other, for the rank of the organisms 
entombed in their strata. 
