134 thf: qufstion of workable 



1. Deep-sea marine formations, consisting for the most part of 

 limestones with marine animal remains, known as the Carboniferous 

 Limestone, passing up into Yoredale shales and sandstones. In some 

 areas (as in Devon) this formation changes its character to the Ctdm, 

 the marine fauna being feebly represented along with a considerable 

 development of a land-flora. 



2. Shore-formations indicating a gradual shallowing of the sea, 

 consisting of grits and sandstones, known in English geology as the 

 Milhtone-grit. 



3. Fresh-water marsh and lagoon formations, broken by insigni- 

 ficant oscillations and occasional shallow sea deposits, consisting of 

 the Coal-bearing strata with land-plants in abundance, the vegetation, 

 where sui^ciently concentrated (chiefly in the middle and upper 

 strata), being mineralised into seams of coal, which together with the 

 sandstones and shales form the productive Coal-tneasures. 



[The maximum thickness of the Millstone-grit and Coal-measiu-es 

 in Britain exceeds 15,000 feet.] 



4. Shore formations, consisting chiefly of conglomerates and 

 sandstones, bearing workable coal-seams in some parts of Europe, 

 and indicating gradual subsidence (of more limited areas than in t) 

 generally 2vith a stratification quite discordant ivith that of the older 

 formations. This is the Roth/iegendes, or Lower Dyas of German 

 geologists. 



5. Deep-sea marine formations, consisting for tjie most part of 

 limestones with marine animal-remains, \.\\e Magnesian Limestone of 

 the north of England, the Zechsiein of Germany. 



The storage of carbon in the lithosphere of the earth in the form 

 of the mineralised vegetable- matter of our coal seams is not confined 

 to one stage of the earth's history, but it is to be found so concen- 

 trated at that stage as to exceed the aggregate amount of the work 

 done of this nature through all other periods put together ; and no 

 name in geology has, perhaps, been more felicitously chosen than that 

 which is universally given to the great Carboniferous System. How 

 was this brought about ? There must have been a cause, and recent 

 researches have brought the cause to light. We must recollect that 

 the small quantity of carbonic acid gas (about four parts in 10,000) 

 in our present atmosphere is no measure of what existed in the 

 atmosphere of palaeozoic times, for the simple reason that all the 

 carbon of our coal-seams, all the carbon of the later (Tertiary) Brown 

 Coal deposits, all the carbon locked up in the present vegetation and 



