690 THE WONDERS OF GEOLOGY. Lect. VII. 



are, however, confined to small areas : as in the Depart- 

 ment of the Loire, at Brassac, in Silesia, and many other 

 places. All these deposits have been formed in lakes, 

 existing in the islands of that sea in which the mountain 

 limestone was deposited.* 



Throughout the Russian Empire the productive coal 

 beds are situated in the mountain limestone : but in 

 Poland and Silesia, the coal measures are interstratified 

 with shales and sandstones which overlie the mountain 

 limestone, as in England and Belgium. 



The Russian carboniferous strata are unquestionably 

 fluvio-marine ; for through a thickness of eight hundred 

 feet, limestones, grits, and shales, abounding in marine 

 shells, alternate with beds of coal. The vegetables of 

 which the coal is formed, consist of broken and drifted 

 plants, carried into the sea by inundations and freshes of 

 rivers ; the layers of clunch or finely levigated shale which 

 support the coal-seams, may have originated from the 

 earthy debris brought down by the floating masses of ter- 

 restrial plants, t 



* Mr. LyeH's Elements of Geology. 



f Sir R. I. Murchison. — The following remarks of an eminent 

 French geologist, M. Constant Prevost, are especially worthy of 

 attention in relation to this subject : — " On n'a pas assez reflechi 

 lorsque Ton a dit que les formations fluvio-marines n'Staient que 

 des accidents locaux d'embouchure et de golfe j on pourrait presque 

 avancer, sans paradoxe, que dans certaines mers bordecs de vastes 

 continents, les eaux douces affluences produisent plus dans la 

 mer, que les eaux marines elles-memes. Le Mississipi et ses tri- 

 butaires enlevent au continent qu'ils travcrscnt, plus de matures 

 sedimentaires et de corps organises, pour les porter dans la mer, que 

 les vaguas de celles-ci n'en prennent sur tout le pourtour des deux 

 Ameriques ; et Ton sait, par de journaliers cxemplcs, que de* vege- 

 taux apport6s par ce flcuve, des rives du Missouri dans le golfe da 

 Mexiquc, vontatterir sur les coirs d'Islande, et meme du Spitzberg." 

 — De la Chronologic des Terrain* et du Synchronisms des Forma 

 tioits. 1845. 



