244 THE MENDirS: A GEOLOGICAL REVERIE. 



and other marine creatures ; and this, notwitiistaiuiing tliat 

 the sea-bed was undergoing steady, though it may be un- 

 equal subsidence. Then, in course of time, the waters of 

 tlie northern part of the Mendip Sea became more turbid, 

 and sandstones and shaley beds were interstratiiied with 

 the limestones ; for we must remember that rain and the 

 weather, aided perhaps in the uplands by giant frost, were 

 doing their worst upon the bordering continental land, and 

 great rivers were washing down the resulting debris into 

 the land-locked seas. Thus by the deposition of limestones, 

 shales, and the millstone grit the Mondip Sea was silted up, 

 and throughout the mediterranean area there was formed 

 a series of enormous swamps, on which there sprang up a 

 rich and luxuriant vegetation of ferns and giant club-mosses, 

 and tall Anted reeds, among which great stupid, shovel- 

 headed, salamander-like labyrinthodonts "pottered, like 

 Falstaff in his old ago, with much belly and little log." 

 From time to time submergences took place, like that 

 which in 1811-12 converted a huge area of the Mississippi 

 delta into a vast sunk country. But ere long the sub- 

 merged tracts were again silted up ; the rank vegetation 

 obtained onco more a foothold ; and fresh accumulations of 

 peaty and other vegetable matter were formed, only to be 

 again, by reiterated submergence, more and more deo]>]y 

 buried beneath silt and sand, and thus to be stored as coal 

 for the future use of man. 



How long this state of things continued it is impossible 

 to say. But we know that there was time enough for the 

 coal measures in South Wales to attain a thickness of from 

 ten to twelve thousand feet with seventy-five seams of coal. 

 It was a period when geographical changes were slight, 

 when terrestrial disturbances were at a minimum, and when 

 the denizens of sea and land, of marsh and swamp, found 



