

THE TllIAssir SYSTEM :if>r> 



r idea of the component strata, it will be best to deal separately 

 with f.u-li of the two great divisions of the Trias, for only two 

 c\i>t in Britain, the Banter and the Keuper. 



THE BUNTER SERIES 



Tins set of beds has a more restricted range than the Keuper 

 Series, a fact which is not always realised because it is concealed on 

 a geological map by the overlap of the Keuper and the continuous 

 outcrop of the latter all across England from south-west to north- 

 east. The Bunter is not similarly continuous, but was deposited 

 in two separate basins, a northern and a southern. The northern 

 was much the larger of the two, extending from Worcestershire 

 through the Midland counties, and including a large part of 

 Northern England with probably a branch or gulf which reached 

 into the north-east of Ireland and the south-west of Scotland. 

 The southern basin was on the site of the pre-existent Permian 

 lake, covering parts of Devon, Somerset, and the area of the 

 English Channel. 



The typical district of the British Trias is that of the Western 

 Midlands, an area embracing Cheshire, South Lancashire, Shrop- 

 shire, Staffordshire, and Worcestershire. Here the Bunter Series 

 is divisible into three stages as below : 



The Upper Mottled Sandstone, from 200 to 600 feet. 

 The Pebble Beds, 300 ,, 1000 feet. 



The Lower Mottled Sandstone, ,, 200 600 feet. 



In describing these Bunter deposits it will be convenient to 

 begin with this typical district, next to trace their extension to 

 the north and north-east, and, finally, to notice their equivalents in 

 the south of England. 



1. Central Area 



The Lower Mottled Sandstone. In Cheshire and Shrop- 

 shire this is usually variegated in bright red and yellow colours. 

 It generally has a basal breccia about 2 feet thick lying uncon- 

 formably on the Permian or the Coal-measures, but is otherwise 

 devoid of pebbles. It always exhibits much oblique bedding, 

 which has the aspect of current bedding, but is not a proof of 

 deposition in water, for the sands may have been aeoliau, and the 

 bedding be due to the action of wind, for in some of the beds the 

 component quartz grains have the worn face and elongate oval 

 shape which is characteristic of modern desert sands, the grains 

 resembling millet-seed. 



