Rock Salt. 155 



the bones of land lizards, Thecodontosaurus antiquus, 

 Palceosaurus Cylindrodon, and P. Platyodon. 



The rock salt of England lies above these beds in the 

 great marly plains of Lancashire, Cheshire, and Worces- 

 tershire. It is found at varying depths, in interrupted 

 lenticular beds, ranging from a few feet to about 120 

 feet in thickness. No fossils occur in the salt. The 

 mass is usually of a reddish colour, due to the presence 

 of ferruginous impurities. 



For long there was a total absence of any rational 

 account of the manner of deposition of rock-salt, but I 

 think few geologists now doubt that it was precipitated 

 in supersaturated salt lakes during the Keuper period ; 

 and this could only have been done by evaporation, due 

 to solar heat acting on the waters of salt lakes which 

 had no outflow, like the Great Salt Lake of Utah, for 

 example, or the salt lakes of Central Asia and of the 

 Sahara. 1 The red marl varies from 500 to 2,000 feet 

 in thickness, and contains a thin band of white sand- 

 stone, often with pseudomorphs of crystals of rock-salt, 

 and also bearing a small bivalve crustacean, Estheria 

 minuta, a lamellibranchiate small bivalve shell, Pul- 

 lastra arenicola, a fish, Hybodus Keuperi, footprints 

 of Labyrinthodon giganteus, and others, also bones of 

 reptiles, and traces of land plants, fig. 33. Teeth also of a 

 small Marsupial mammal, Microlestes antiquus, occur 

 in the red marls near Watchett in Somersetshire. This 

 is the oldest known mammalian relic. In Scotland, 

 at Lossiemouth, Keuper sandstones contain scutes and 

 bones of a crocodile, Stagenolepis Robertsoni, Hypero- 

 dapedon, and a land lizard, Telerpeton Elginense.* 



1 See memoir < On the Physical Relations of the New Bed Marl 

 Ilhaetic Beds, and Lower Lias : ' Geological Journal, 1871 : Ramsay. 



2 On the Continent, near Strasburg, abrut thirty species of plants 



