320 STEATIGRAPHICAL GEOLOGY 



limestones being interbedded with marls and sandstones, clays and 

 layers of gypsum ; and the highest beds contain a Stephanian flora 

 (Pecopteris arborescens, Annularia longifolia). 



The Uralian Sea must have occupied the greater part of Kussia, 

 passing southward over the Crimea and south-eastward through 

 the Balkans, Bosnia, Herzegovina, Carniola, and the Julian Alps. 

 Farther west, in the Carnic Alps between Italy and the Tyrol, 

 there is an interesting intercalation of the Uralian and Stephanian 

 facies, i.e. of freshwater and marine beds. The following series has 

 been described by Schellwein at Krone : n 



Shales with Spirophyton. 



Dark-grey limestones with Fusulina and Swagerina. 



Sandstone with Pecopteris and Annularia stellata. 



Bed containing marine shells. 



Shales witli Annularia stellata and other plants. 



Shales and calcareous sandstones with Camarophoria, Productus, and 



Phillipsia. 



Shales with Pecopteris oreopteroides. 

 Conglomerates at base (about 200 feet thick). 



The total thickness of these beds is about 900 feet, and they are 

 overlain by another Fusulina limestone which is of a light-grey 

 colour and contains a Lower Permian fauna. How much farther 

 west the Uralian Sea extended is not yet known, for no marine 

 strata of this age have been found in Italy or Spain, though 

 deposits with a Stephanian flora occur in both countries. 



C. THE FORMATION OF COAL-SEAMS 



The most important point connected with the deposition and 

 distribution of the Coal-measures is the formation of coals ; what 

 they are made of, and how they were accumulated. The reader 

 will find this subject well treated in a little book, On the Natural 

 History of Goal (Camb. Univ. Press), \>y Mr. N. Arber, but a 

 brief summary of the current theories and modern views respecting 

 the origin of coal may here be given. 



A complete explanation of coal-seams must account for (1) the 

 source of the carbonaceous material ; (2) the different existing 

 varieties of coal ; (3) the frequent alternations of coals, clays, 

 shales, and sandstones ; (4) the great extent of some single beds of 

 coal. The reader is probably aware that there are many kinds of 

 coal which go by different names according to their chemical com- 

 position and physical peculiarities. There is so-called " Brown- 

 coal," which is little more than lignite or fossil wood ; there 

 is glossy Cannel coal, which does not soil the fingers and burns 

 with a clear, continuous flame ; there are the Humic or so-called 



