001 GEOLOGY OF THE WESTERN COALFIELDS, 



I may here repeat, perhaps ad nauseam, that this is our last 

 marine formation, so far as the Coalfields are concerned, and that 

 all our subsequent sedimentary rocks are either of fresh-water or 

 subaerial origin, j^ow wherever the rocky sea-bottom fell steeply 

 from the shore, it would be impossible for this sh'elly sand to 

 accumulate, except in small patches. And wherever the water 

 was deep enough and far enough from the shore neither sand nor 

 shells would be formed. It would therefore be reasonable to 

 expect that such a formation should have many breaks or gaps 

 in its extent, and that m consequence the subsequent deposits 

 which owe their preservation to the fair level foundation which 

 it provided, should have been chequered with a similar pattern of 

 deep spaces or lakes of fresh water, in which but little sediment 

 could deposit itself. Por in lakes there are no great and con- 

 tinuous currents, as in the Ocean, to carry river detritus hundreds 

 of miles away from the place where it was discharged. Sands 

 brought down by rivers into lakes accumulate in deltas and flat 

 banks with their fronts sloping sharply down into the deep water 

 bevond ; while even the finest particles of muddy cloud, slowly 

 as they sink, will very soon have fallen through the stream in 

 which they were supported, as it slackens, widens and thins out 

 in the lake, and will then find themselves in dead water through 

 which they can only sink vertically, whatever length of time they 

 may require to reach the bottom. Consequently lacustrine 

 deposits must always be marginal. 



After a long period during which the energy of glacial and 

 other erosion seems to have been gradually diminishing, we turn 

 our eye again upon the scene. We observe that the Alps are lower, 

 the plains more level and broad, stretching out as an almost level 

 shallow bottom beneath the waters of tranquil lakes, which have 

 taken place of the sea. There is no sea in sight. The landscape 

 is one of a multitude of fresh-water lakes bordered by level plains 

 through which gentle rivers flow from the hills behind. Vegetation 

 is abundant, though apparently of a rather dwarfish or stunted 



