662 



THE WONDERS OF GEOLOGY. Lect. VII. 



characters of the beds of coal interpolated in the strata, 

 that were deposited during the ages intervening between 

 the close of the Devonian epoch and the commencement of 

 the Permian.* 



The strata comprised in the carboniferous system form 

 three natural groups, as shown in the following table ; and 

 I propose to consider, in the first place, the general fea- 

 tures of the deposits, and their geographical distribution ; 

 secondly, the nature and formation of coal, and the charac- 

 ters of the fossil plants of which it is composed ; and, lastly, 

 notice the animal remains, and take a retrospective view of 

 the successive floras which have prevailed on the surface 

 of the earth, during the epochs embraced by our geological 

 investigations. 



2. The Carboniferous System. — The following tabu- 

 lar arrangement exhibits the lithological characters and 

 relations of these deposits : — 



I. The Coal measures. Sandstone, shale, and grit, with numerous 

 beds and layers of Coal ; ironstone in nodules, and irregularly 

 stratified. Intercalations of bands of limestone, with fresh- 

 water shells and crustaceans. Total thickness, upwards of 

 1000 yards in some districts. 



II. Millstone grit. Coarse quartzose sandstone passing into a 



conglomerate used for millstones — hence the geological term ; 

 with shales and sandstones ; containing interspersions of fossil 

 plants and vegetable matter, and sometimes layers of coal. 

 Total thickness, about 600 feet. 



III. Carboniferous or Mountain limestone. A series nearly 1000 

 feet in thickness of limestones and flagstones, containing corals, 

 crinoideans, and marine shells in profusion. Beds of marble 

 wholly made up of petrified zoophytes. Numerous cephalopoda 

 and brachiopoda. This group is generally devoid of coal in 

 England; but the mountain limestone of some parts of Russia 

 contains extensive coal-mines. 



The Mountain-limestone group rests upon the Devonian 



* See remarks on the Coal of the Oolite, ante, p. 514 ; of the Weal- 

 en, p. 392; of the Tertiary, p. 27S ; and in peat, p. 60. 



