256 



LYELL'S ELEMENTS OF GEOLOGY. 



Origin of the Coal Strata. 



enveloped in sediment. It is more probable that a large part of 

 them were deposited immediately with the mud and sand swept 

 down with them by rivers into lakes or the sea. This must have 

 happened in those rare cases where the ferns still retain their 

 fructification. Where this has disappeared, its decomposition 

 may often have been subsequent to the inclosure of the frond in 

 mud or sand. 



Origin of the Coal strata. — Detached portions of the ancient 

 Carboniferous group extend from Central Europe to Melville 

 Island and the confines of the arctic region ; but do not appear 

 in the south of Europe ; for the lignite and coal found south of 

 the Alps and Pyrenees, in Spain, Italy, Greece, and other coun- 

 tries bordering the Mediterranean, seem referable to the Creta- 

 ceous and other comparatively modern groups. 



It has been already shown that, in some parts of England, as 

 in Shropshire, certain Coal-measures consist of freshwater strata, 

 and may have originated in a lake, while others, not far distant, 

 were deposited in estuaries to which the sea obtained access 

 occasionally ; while a third class were formed at the bottom of 

 an open sea, or in bays of salt water into which land plants were 

 drifted.*' 



In many parts of France and Germany there are isolated 

 patches of Coal strata, entirely free from marine fossils, which 

 repose on granite and other hypogene rocks. They are often 

 confined to an extremely small area, as at St. Etienne, in the 

 department of the Loire ; at Brassac, in that of Puy de Dome ; 

 at Sarrebruck ; also in Silesia ; and a hundred other places. 

 All these deposits may have been formed in lakes, existing in 

 the islands of that sea in which the Mountain limestone was 

 formed, t 



If the climate of New Zealand and the surrounding ocean was 

 warmer, so that tree-ferns could thrive more luxuriantly on the 

 land, and corals build reefs in the sea, v/e might conceive new 

 strata to accumulate in that part of the globe analogous to those 

 of the ancient Coal. The two islands of New Zealand are be- 

 tween 800 and 900 miles in length ; and through the middle of 

 them runs a lofty chain of mountains, said in some parts to be 

 14,000 feet high, and covered with perpetual snow. Many 

 rivers descend from their sides ; and, in the spring, these are 

 copiously charged with sediment, and with abundance of drift 

 wood. Opposite the mouths of these rivers, and near the shores, 

 wherever these may be wasting by the action of the waves, an 

 irregular zone of gravel, sand, and mud, must be forming in the 



* Murchison, Silurian System, p. 148. t Burat's D'Aubuisson, torn. ii. p. 268. 



