SALTER- 
: — A CHRISTMAS LECTURE ON COAL. 
59 
on the descendants of the parent type, although it would not be 
possible for me fully to subscribe to Darwin's theory — which I do not 
perfectly realise, without much fui'ther examination and reflection 
— still there is so much truth in many of his views and statements 
regarding " The struggle for existence" and " principle of natural 
selection," that the subject has full claim to a calm and dispassionate 
examination, and may lead us by degTees to the better understanding 
of many problems relating to species and their origin than we at 
present possess. 
A CHRISTMAS LECTURE ON "COAL" 
By J. W. Salter, F.G.S. 
(Continued from page 13. J 
In our last lecture stress was laid on the fact that coal-beds, unlike 
mineral veins, are stratified — not injected, or filling cracks in the earth 
as metals do. And when we use the term stratified, we mean that 
the materials we are considering — coal, ironstone, sandstone, clay, 
shale — were all deposited sheet over sheet, layer over layer, principally 
by the agency of water. 
In scarcely any other way, except by water, can we conceive of 
materials being spread abroad over vast surfaces, in that even and 
regular manner which we call " stratified." As a rule, the matters 
ejected from the mouths of fiery volcanos are only mdely heaped up, 
and unless they fall into the sea, do not undergo this smoothing, 
spreading-out process. The sand of the sea-shore however, and the 
pebbles on its margin, and the mud of its great depths, are truly 
" stratified;" and if a fertile plain, or a marshy district were submerged 
in the waters, the materials on that surface would be soon covered 
over by the ooze and sand and shingle, and would then be said to be 
" interstratified" with them. In this way coal-beds occur among 
beds of sandstone and other rocks. 
It is seldom that any coal-field contains more than twenty-five or 
thirty workable seams : and perhaps these altogether do not amount 
to above eighty or one hundred feet at the utmost, while in South Wales 
the coal strata are twelve thousand feet thick. The mass, you see, is 
rock. 
The miners have names for all the other beds, or " measures" as 
they term them. Some of them are amusing. In Staffordshire, 
for instance, the beds of sandstone (once loose sand) receive the names 
of White, grey, green, and blue rock; Rough rock; and " Peldon." 
This last is a very common term. 
