loo The American Geologist. February, i904. 
in old age or of completed evolution, but is an example of 
arrested development. The moon's growth was stopped by- 
lack of building material before its gravitational power was 
competent to hold an atmosphere. Its internal heat was ap- 
parently sufficient and its volcanic action pronounced, but its 
gaseous exudations seem to have been lost into space or frozen 
at the surface. If the planetesimal hypothesis be true in its 
postulate of world origin and growth then in the moon we may 
have a visible illustration of an early stage in the process. 
The mineral contents of sea water are held by the old hy- 
pothesis to be derived from decay of primitive rocks except to 
whatever extent they were indigenous to the nebulous envel- 
opes. The new hypothesis allows derivation in part from su- 
perficial rock alteration, specially the carbonates, but suggests 
emphatically that most of the saline mineral content of the 
ocean has been derived, like the ocean itself, from subterranean 
sources. 
EARLIEST SEDIMENTARY ROCKS. 
Under the conception of a globe cooling from a superheat- 
ed state the conclusion seems inevitable that the first deposits 
should have been chemical precipitates from the ocean of hot 
water. This idea has been the subject of speculative writing, 
but no rocks have been found which appear to have had such 
genesis, although if such precipitates were ever formed they 
should be discovered somewhere in recognizable form. The 
conception has been barren of results in petrography. 
The nebular hypothesis requires that the globe should have 
been fully formed before the surface or epigene agencies began 
their work, and that all the vast deposits of fragmental origin, 
the clastic rocks, have been wholly derived from the primitive 
land areas by rock destruction. The new hypothesis allows a 
different view. "According to this the ocean began its work 
long before the earth and moon had attained full size by gath- 
ering to themselves all the particles of the earth-moon ring or 
zone. Consequently there were oceanic sediments which were 
not wholly detrital, but were primitive world-stuff. The earl- 
ier ocean sediments must have been deeply buried under the 
later, and may now constitute part of the interior mass of the 
globe. It may be that the globe had attained full size before 
anv of the visible clastic rocks were made. With the water 
