Lower Lias. 167 



forms of these island territories were even approximately 

 identical with those of the present mountains, and 

 the limits and orographic contours of these fragments 

 of an old physical geography can only be approximately 

 guessed at. They have undoubtedly been subjected to 

 repeated disturbance and upheaval since the beginning 

 of the deposition of the Lias, but after these old 

 palaeozoic mountains first rose high into the air, they 

 suffered so much from all the agents of waste and 

 degradation, that in Liassic and pre-Liassic times, I 

 have no doubt they were higher than now, and partly 

 occupied more extended areas. 



THE LOWER LIAS CLAY AND LIMESTONE is about 

 900 or 1,000 feet thick, where best developed in England, 

 and consists of beds of blue clay or shale (weathering 

 brown), interstratified with beds of blue argillaceous 

 limestone, largely quarried in Leicestershire, Warwick- 

 shire, and elsewhere, for hydraulic lime. These lime- 

 stones, lying flat and unconformably on the upturned 

 and denuded edges of the Carboniferous Limestone, 

 form splendid cliffs on the coast of Glamorganshire, 

 and, with the Khsetic beds, they are also well exposed 

 in the coast section at Lyme Regis. From thence, 

 scarcely interrupted at the east end of the Mendip 

 Hills, the Lower Lias strikes north to the junction of 

 the Severn and Avon, and again NE. and N. to the 

 sea-coast of Yorkshire, E. of the river Tees. Through- 

 out this area it usually forms a flat or undulating 

 country, lying much in pasture land. The strata dip 

 generally gently to the east, but are sometimes for a 

 space quite flat. Occasionally the limestones of the 

 Lower Lias form a low escarpment, generally facing 

 west, and, almost invariably, the Marlstone or Middle 

 Lias makes a similar and higher escarpment, the top 



