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 further 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 degrees 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 IS.) 



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 rudely 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 

 " inter stratified" 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 sancl) receive the names 

 of White, grey, green, and blue rock; Rough rock; and " Peldon." 

 This last is a very common term. 



