66 THE DOCTRINE OF DESCENT. 



one chalky (mountain limestone), the middle one con- 

 glomerated or arenaceous (millstone grit), and the up- 

 per one carboniferous (coal measures); hence a marine, 

 a littoral and a marsh or fresh-water formation. It is 

 easy to imagine the cause of this phenomenon; it de- 

 pends on the secular elevation of the primaeval sea bottom, 

 on which was deposited first the marine mountain lime- 

 stone; secondly, as it rose to the surface, the shingle 

 and coarse sand of the shore; and finally, on persistent 

 elevation, the products of marshes, lagunes, and estuaries. 

 If it now happened that some portions of the infant con- 

 tinent covered with the latter (that is to say, with the 

 productive carboniferous strata), were seized with an op- 

 posite movement, and therefore sank, there would be 

 deposited on the surface now again gradually becoming 

 the bed of the sea, precisely similar forms, only in in- 

 verse order to that which occurred during the period of 

 elevation. 



And, in fact, this phenomenon is exhibited by those 

 portions of the earth's surface which shortly after the 

 formation of the coal measures again sank below the 

 sea. In Germany and England the productive coal meas- 

 ures are followed by a sandstone and conglomerate, there- 

 fore a littoral formation, exactly like the quartzose sand- 

 stone and millstone grit which underlies them ; and above 

 this a limestone, dolomite and gypsum formation, corre- 

 sponding to the mountain limestone, the lowest member 

 of the carboniferous system. On account of the division 

 which is displayed in profound palseontological and petro- 

 graphical diversities, the formation thus developed and 

 composed is designated as the Dyas. The separate 

 phases of this cycle of occurrences, by which the car- 



