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POPULAR SCIENCE REVIEW. 
open question, for when we take into consideration the great 
changes it must have experienced during countless ages, and 
the vast amount of “ debris ” directly or indirectly the result 
of its wear and tear, which has been scattered all over the globe, 
we can have no reason to expect to meet with any portion of it 
in situ iu any part of the world ; as, however, quartz is found 
to be the most preponderating of all the minerals composing 
the most ancient rocks, this fact confirms the view that the 
original crust must have been extremely rich in silica, much of 
which no doubt would separate out from the other constituents 
in the form of quartz during the act of solidification. 
From this time up to the present age all the various changes, 
whether of mechanical or chemical origin, which have taken 
place in our globe have been brought about by agencies identical 
with those which we now see in operation, although possibly on 
a somewhat different scale; stratified rocks became formed 
from the wear and tear of the primitive crust by aqueous 
action, precisely as at the present moment we see them recon- 
structed from the “debris” of preexisting rocks of all kinds; 
the quartzites of the older rocks were formed from the com- 
minuted quartz out of the primitive crust, just as the later sand- 
stones and grits, whilst the associated silicates owing to the 
action of carbonic acid and water would be more or less decom- 
posed, thereby producing beds of clay and others of areno- 
argillaceous character, whilst the largest proportion of the 
alkalies contained in them, would in the state of carbonates be 
carried off in solution by the water to the ocean, where they 
would react upon and decompose any chlorides or other salts of 
the metal, or earths which they might encounter. 
Whilst all these changes were in progress, outbursts of fluid 
mineral matter from the still molten interior of the earth would 
from time to time continue to break through and disturb the 
primitive crust, and the rock strata in course of construction 
above it, exactly as we at present see similar eruptions from 
volcanic centres, and as many of these would then as now take 
place at parts of the crust covered by the ocean, they would 
result in production of vast volumes of submarine tufas and 
breccias which by the action of the waves would at once assume 
the form of ordinary stratified formations. 
With the exception, however, of some minor occurrences of 
calc-tufas and precipitated carbonate of lime, no calcareous or 
limestone beds were deposited during this early period, nor 
were carbonaceous beds of any kind in course of formation, for 
the simple reason that both these classes of deposits owe their 
origin to the action of animal and vegetable organisms. 
The atmosphere of this stage in the earth’s history was, 
however, vastly different from what it is at present : instead of 
