Trias and Lias 51 



The oldest member of the series is the Trias. This 

 Trias forms a broad area, broken by islands of 



older rocks, in the very centre of the country. 

 Besides its long northward outcrop on the eastern flank 

 of the Pennines, extending to the Durham coast, and 

 its southward outcrop — narrow and somewhat inter- 

 rupted—to the coast of Devon, it has an important north- 

 westward extension, separating the Palaeozoic rocks of 

 the Pennines from those of North Wales, and reaching 

 the Irish sea on the coasts of Cheshire and Lancashire'. 

 Speaking broadly the Trias forms low ground: to the 

 north the plain of York, to the north-west the plain of 

 Cheshire, and in the centre the Central Plain of England. 

 It has two main divisions in England, the Bunter, con- 

 sisting of sandstones, and the Keuper, mainly of marls, 

 the " Muschelkalk " of the Continent being absent from 

 this country. The Bunter sandstones form a poor soil, 

 woodlands of the oak-birch series and heathland, as 

 in Sherwood Forest in Nottinghamshire and Delamere 

 Forest in Cheshire, occurring on these beds. The Keuper 

 marls form fine meadow and pasture land, for instance 

 in Cheshire. 



The Lias comes next, extending from the coast of 

 Dorset to the coast of Yorkshire. Like the Trias, its 

 greatest extension is in the Midlands, where it forms part 

 of the plain of central England. The Lias consists of clays, 

 marls, shales, and more or less pure limestone bands, and, 

 locally, some sand and sandstone. It forms mainly flat 

 country, with low escarpments, representing the limestone 

 bands, in places. The clays and marls give fertile agri- 

 cultural country, with rich pasture-lands. 



The vegetation of the Keuper and Liassic marls of 

 Somerset has been studied by Moss^; he found that 

 (ash-)oak-hazel wood (see p. 182) and calcareous pasture, 



1 With small isolated tracts occupying the Eden valley in Cnmberland 

 and the Vale of Clwyd in Wales. - Moss, 1907, p. 50. 



4—2 



