568 Revieics — J. B. Simpson — N ortliumberland Coal-field. 
and a sinking of the waters to their present level. By this latter 
action we had the water, so to speak, split. up into separate areas. 
This would explain the similarity in the fauna of the different 
districts, should it ever be proved satisfactorily to exist, and also the 
presence of salt lakes in the Trans-Baikal territory, where the 
waters, for want of outlet, have become gradually supersaturated, 
until now they annually form a deposit on their shores. 
Most of what I have said about the Baikal, it will be seen, is based 
on scanty evidence, and must only be accepted until something better 
can be obtained. When the geology and zoology of these districts 
have been further investigated, it remains to be seen if we get in- 
dications as to the origin of the physical features of tbis part of the 
world still pointing in the same direction, as those do which we 
have at present in possession. 
So far, then, I am content to believe that at one time, in this 
portion of the world, there were inland fresh waters which deposited 
alluvium, and, as these retired, the Baikal, with its surrounding 
lakes and lakelets, were left like pools behind a flood. 
EEVIEWS. 
I. — Sections of the Northumberland and Durham Coal-field. 
By J. B. Simpson, M.E. (Large folding sheet, publislied by A. 
Keid, Newcastle-on-Tyne, 1877.) 
T HE times when mining engineers jealously kept their local know- 
ledge to themselves are rapidly passing away, and it is but rarely 
now that information of a scientific character is withheld from the 
public. The publications of the Greological Survey teem with acknow- 
ledgments of assistance rendered by the very men who, years ago, 
would have thought it their duty to oppose obstacles to the progress 
of such work. There are still exceptions, but they are few and 
far between — survivals, but not of the fittest. The issue of the 
handsome sheet before us is a case in point. Here Mr. Simpson, 
well known as one of the most active of North-country mining 
engineers, and the author of more than one paper of geological 
interest, has given the world a key to the structure of the great 
Northern Coal-field, of which it is difficult to speak with sufficient 
praise. In the right-hand corner of the sheet an index geological 
map shows the limits of the field, its chief lines of fault and the 
lines of section, one N. and S., and the other E. and W., the 
detailed illustration of which forms the chief object of the plate. 
This object is attained by means of nearly fifty actual measured 
vertical pit-sections carefully drawn to scale, and placed side by side 
in order across the sheet. To the left Stands a general section in 
which every recorded Coal-seam is given and numbered, correspond- 
ing numbers being used in all the other sections for the same beds, 
thus enabling one to ascertain at a glance the author’s views as to 
the equivalence of the minor seams. This is perhaps the most 
valuable feature of the publication. As a datum-line the Low- 
Main or Hutton Seam has, we think very properly, been chosen. 
