550 THE AMERICAN NATURALIST. [VoL. XXXIII. 
across a mountain range as it was slowly being elevated, and contin- 
ued its course far out into what is now the present ocean, to a point 
at least eighty miles eastward of Long Island. In late geologic 
time a downward movement of the earth’s crust, too insignificant to 
be noticed in comparison with the whole diameter of the earth, has 
brought the former mouth of the river below sea level, and the salt 
water gradually encroaching has filled the broad valley where now is 
the important harbor of New York, and has made possible ocean 
navigation far inland. The influence of this easy route of communi- 
cation up to the site of the present city of Albany, and from that 
point by easy paths up the broad Mohawk to the Great Lakes, 
determined the history, not only of New York State, but of the 
people of the continent, and has resulted in making this state the 
richest of the American Union. dae Bo ee re 
PETROGRAPHY. 
The Volcanics of San Clemente. — San Clemente Island, off the 
coast of Southern California, is built up* almost exclusively of lava 
flows, volcanic breccias, and ash deposits. The principal eruptive 
is a pyroxene-andesite. In addition to this, there are smaller areas of 
rhyolite and dacite. The andesite consists of a mediumly basic 
plagioclase, augite, often hypersthene and magnetite as phenocrysts 
in a ground mass composed of the same minerals, with a larger or 
smaller proportion of glass. The dacite lies above the andesite, and 
the rhyolite above the dacite. The former rock contains the same 
phenocrysts as the andesite, but in the ground mass there is consid- 
erable quartz intergrown with oligoclase in micropoicilitic patches, 
and a large quantity of orthoclase, likewise in micropoicilitic inter- 
growths with the same plagioclase. The quartz and orthoclase 
appear to form the matrices in which laths of the plagioclase are 
imbedded. 
The rhyolite is of an unusual type. It comprises phenocrysts of 
andesine, a few of hypersthene and magnetite, and an occasional one 
of augite in a microgranular and glassy matrix. The crystalline portion 
of the matrix is composed of quartz, orthoclase, and andesine, form- 
ing bands and lenses separated from one another by bands of glass. 
1 Smith, W. S. T. Eighteenth Ann. Rep. U.S. Geol. Survey, 1898, Pt. ii, 
P. 459- 
