1878. | The Microscope in the Examination of Rocks. 15 
with forms of which it is difficult to decide without the aid of the 
microscope and some preliminary preparation of his material, 
whether they have to be treated by the lithologist or palzontolo- 
gist. A chemical analysis will not disclose their origin, whether 
by mineral accumulation or organic life. Usually they are left 
to the lithologist who, not long ago, claimed all the fossils as 
freaks of nature. A great number of those interesting forms are - 
generalized with oolites, concretions, etc. The unsatisfactory re- 
sults obtained by the limited macroscopical and chemical 
analysis of rocks and fossils, induced Dolomien and Cordier 
in the last century to advocate the use of the microscope as a 
necessary and important instrument for investigations in geo- 
logy. But their efforts failed to secure to the microscope an 
acknowledged position in the laboratories of the lithologist and 
paleontologist. This failure has to be principally attributed to 
their defective mode of preparing the rocks for the micro- 
scope. The examination of the rock consisted mainly in view- 
ing its natural fracture or polished surface by aid of reflected 
light, as the opaqueness of the material did not allow the use of a 
transmitted light. This imperfect method could not be of much 
service. 
Another method of preparing rock material for the microscope 
was to crush it to a fine uniform powder, which by decantation 
with water was deposited according to its specific weight. The 
minerals composing a compound rock being of different specific 
weight, they separated in beds or layers, which contained prin- 
cipally one and the same mineral. The minuteness of the powder 
allowed it to be viewed under the microscope with transmitted 
. = light. In most cases the minerals could be recognized either by 
means of the magnifying power or by aid of chemistry, which 
analyzed the separated layers by themselves, but which in reality 
do not always consist of fragments of the same kind of mineral, 
but are also partially mixed up with each other. The chemical 
analysis could not be entirely depended upon, but had to be veri- 
fied by microscopical observation. The greatest drawback to 
this method of rock analysis is the entire loss of structure during 
_ the grinding process. And although Ehrenberg, by this method 
of examining rocks in form of dust, achieved his famous results 
of the micro-fossil organs of the chalk formation, yet the micro- 
‘scope remained for a long time of only limited use. 
The great reorganization of lithology which has recently been. 
