Nezv Hypothesis of Earth-Origin. — Fairchild. loi 
on the earth's surface increasing by supplies from the interior 
and with matter still being gathered in from the exterior, the 
depressions of the primitive continents were more or less filled 
by a mixed class of sediments partly from volcanic and partly 
from the material of incoming planetesimals. Encroachments 
of the ocean on the continents probably occurred as in later 
times, followed by withdrawals as the ocean basins sank and 
increased their capacity. As the decomposition of the clastic 
material was probably less complete than in later times, from 
lack of vegetal covering and other causes, the mixed sediments 
when metamorphosed resembled original igneous rock, and it 
is now difficult to distinguish the metamorphosed elastics from 
true igneous rocks. '"'^ 
\\^ith the passing of the old hypothesis it will be desirable 
to change the terminology of the rocks as far as this now im- 
plies an original molten or "igneous" state of the earth. Some 
new name will be desirable for the sediments which were 
formed chiefly or wholly from the planetesimals (the cosmic 
matter) in the early seas of the growing globe. Let us call 
such deposits cosinoclastics, and the primitive massive rocks, 
the cosinics. The downward succession of the rocks would 
thus be. from unaltered elastics through altered elastics (me- 
tamorphics) to metamorphosed cosmoclastics ; while beneath 
these, perhaps ever mvisible, lie the altered cosmics, the prim- 
itive deposits. 
The above theoretical succession of the strata, the slow 
upward gradation from primitive world-stuff into the dififeren- 
tiated secondarv sediments seems in better accord with our 
knowledge of the deep-seated rocks than the assumptions of 
the old hypothesis. 
VOLCANIC THENOMEXA. 
The vast extrusions of molten rock over the earth's sur- 
face without explosive phenomena, and the intrusions into the 
superficial zone known as dikes, sills and laccoliths, may be in 
harmony with either hypothesis of world genesis, as the main 
factors seem to be great internal heat, potential fluidity, relief 
of pressure and hydrostatic equilibrium. However, under the 
old hypothesis, which favors homogeneity in the interior, it is 
difficult to see why an outflow of molten rock once begun 
• Quoted from LeConte's Elements of Geology, 5th edition, page 299. 
