220 Reviews—The Coals of South Wales. 
a plentiful supply of water which, while containing a slight amount 
of mineral matter, is absolutely free from any hurtful bacteria, or 
from organic germs of any kind. 
The porous limestone into which these wells are sunk, and from 
which the water rises, extends to the north and west beneath a layer 
of Boulder-clay, and rises to the surface in a number of places in the 
country between Lakes Winnipeg and Manitoba at elevations varying 
from about fifty to one hundred and fifty feet above the level of the 
prairie at Winnipeg. The rain falls on these bare rocky areas, as 
well as on the adjoining clay-covered country, but instead of flowing 
away in rills and streams, as it does on the clay-covered country, it 
at once sinks into the porous limestone and flows through this 
limestone southward and eastward until it finally reaches the surface 
either in the large springs north of Winnipeg or through the wells 
at the city of Winnipeg itself. The quantity that flows from these 
springs and wells is therefore largely limited to the amount of the 
rainfall on those portions of the surface where the porous limestone 
is uncovered. Where it is covered, as it is in many places, most of 
the water derived from the rain either stands in small lakes and 
evaporates from the surface, or drains off towards Lake Winnipeg or 
Lake Manitoba by the many streams which unwater the country. 
The underlying porous limestone through which the water percolates 
on its way from the exposed areas north-west of Winnipeg to the 
wells in Winnipeg is a magnificent natural filter which is protected 
from contaminating influences throughout the populated parts of 
Manitoba by a thick covering of impervious Boulder-clay. No other 
city on the continent is provided by nature with such a filter, and 
no city could afford to duplicate it. 
RAV LEw Ss. 
horney 
I.—Memorrs oF THE Grotoeicat SurvEY oF ENeLAND and WALES. 
Tur Coats oF Sourn Wats, WITH SPECIAL REFERENCE TO ‘THE 
Origin and Disrripurion or AntHracireE. By AuBrey SrraHan, 
M.A., Sc.D., LL.D., F.R.S8., and W. Pottarp, M.A., D.Sc., F.1.C., 
assisted by E.G. Raptry. 2nded. 8vo; pp. 78, with 10 plates. 
1915. Price ls. 6d. E. Stanford, Long Acre, or any agent for the 
sale of Ordnance Survey Maps. 
WITH A MAP, reproduced from Plate IV by permission of the Controller 
of H.M. Stationery Office.) 
NOR a long series of years the energies of those geologists who are 
also chemists seem to have been so concentrated upon questions 
of crystallization and the differentiation of igneous magmas that the 
corresponding and equally interesting problems of continuous variation 
in the composition of beds of sediment have remained outside the 
scope of their activities. To the nation sedimentary rocks are at 
least as important as igneous rocks. To our industries they are even 
of greater importance; and to those who have been called in to. 
help in mobilizing home resources of raw materials and providing 
manufacturers with efficient substitutes for sedimentary materials. 
till lately imported in bulk from abroad, the failure to take stock of _ 
this whole class of the nation’s resources has seemed a neglect which 
