METAMOEPHISM. 43 
water never fails^ and wHch keep in constant action the chemi- 
cal forces employed in Natnre^s great laboratory ? 
We know the mode in wliicli the ordinary rocks_, under 
atmospheric influences and without much pressure_, work up 
into stones_, and incoherent mud^ and sand. Would we see the 
effect of pressure upon these — pressure alone without chemical 
action of any kind_, — we have only to use the methods now in 
the hands of the navigator_, for lifting into the light of day^ and 
away from the influence of the sea^ the corresponding mud in 
deep water. The mud lifted from 2^000 fathoms in the 
Atlantic by Dr. Wallich is described as of a plastic consis- 
tence somewhat akin to that of putty_, but the adhesiveness of 
the particles inflnitely stronger.^^ The same material is 
described by Professor Huxley who examined specimens after 
being in bottles for some time_, as an excessively flne light 
brown muddy sediment_, closely resembling flne chalk when 
dried. There can hardly be a doubt that this mud^ which 
under pressure alone is so tenacious as soon as formed^ would 
soon become almost sohd when covered up with a considerable 
thickness of the same material. It would thus become a rock 
closely resembling chalk. 
If we ;take up a small hand specimen of any rock_, and 
examine it with a view to its origin^ we shall at once recognise 
the fact that some essential change has taken place since it 
existed as mud or sand^ as part of a river bed or sea bottom. 
That it once so existed we may often And proof in the remains 
of animals or vegetables^ distributed through the mass_, and even 
making up a deflnite proportion of the whole. The microscope 
will often greatly assist the student in making this out. The 
minute examination of the various particles will often show 
that they have been rubbed and water-worn_, and then 
cemented together by some foreign substance^ such as car- 
bonate of lime_, brought in by water. Some are perhaps the 
cases of those little chambered shells that abound in certain 
parts of the ocean ; or are parts of shells_, corals^ or other hard 
stony cases of marine animals^ ground down by rolling upon 
each other ; or are quartz sand, broken up in a similar manner ; 
or they are mere particles of clay. All these are proofs of what 
is called aqueous origin, but no accumtflation of the same kind 
seems within our experience as happening now. 
Extending our investigation to a series of strata as shown 
in a railway cutting or a quarry, we advance another step. 
The evidence of original formation by water is yet more clear, 
but the beds are often still more unlike what would now be 
seen. The mud brought down by a river, or produced by the 
beating of the waves on a shore, would, if not heaped without 
order, be arranged in order of relative weight of the particles. 
