378 STRATIGRAPHICAL GEOLOGY 



Welsh quartzites, but are identical with those found in the Old 

 Red conglomerates of Scotland, the stones themselves having been 

 originally derived from the Torrid on sandstone. 19 



For a discussion of this matter the reader is referred to the 

 author's Building of the British Isles (1911). Here it is only 

 necessary to remark that these pebble beds do not signify more 

 than a brief episode in the Bunter epoch ; a few abnormally wet 

 seasons would suffice to pile up all the pebbles which are now 

 spread over Shropshire, Staffordshire, and Worcestershire. They 

 had doubtless been accumulated in the higher tributary valleys of 

 the river-system, and when heavy rains turned the streams of these 

 valleys into rushing torrents, the pebbles were swept down into the 

 main river, which, swollen by the floods, was strong enough to 

 carry them for several hundred miles before they finally came to 

 rest in a bay-like curve of the great plain, for the river must have 

 flowed out westward into and across what is now the basin of the 

 North Sea. There it was doubtless joined by other rivers, all 

 combining to form a still larger one which curved southward and 

 ran into the German lake or lagoon. 



That the episode of the English Pebble Beds was not one of 

 much physical importance is proved by the fact that it was followed 

 by a reversion to the preceding conditions, for the Upper Bunter 

 sandstone is so similar in character to the Lower sandstone that 

 outside the area of the Pebble Beds it is difficult to distinguish 

 them, and the sandy facies of the Pebble Beds merges outward into 

 the Upper sandstone. 



In Germany the characters of the Lower Bunter sandstone, its 

 ripple marks, sun-cracks, and rain-prints, show that it was deposited 

 in a large lake, probably of fresh water, and the Middle Bunter 

 must be either lacustrine or terrestrial ; but the case is different 

 with the Upper Bunter, for its red gypsiferous marls are the 

 deposits of saline water, and in Thuringia the inclusion of a marine 

 limestone marks an incursion of the Southern Sea. 



The epoch of the Bunter was brought to an end by a general 

 subsidence of the whole region, the result of which was to bring 

 the sea over the whole of the low-lying Germanic plain. This 

 is the epoch of the Muschelkalk, and the higher level of the 

 British area at this time is indicated by the fact that it was not 

 reached by the Muschelkalk Sea. That sea passed over Hanover 

 and the Island of Heligoland, and probably reached some distance 

 farther west, terminating somewhere below what is now the bed of 

 the North Sea. 



Thus for a time the plains and lakes of the Bunter were con- 

 verted into arms of the Southern Sea, and communication with 



