256 JURASSIC. 



LIAS. 



The term ' Lias ' is supposed to be the corruption of a word 

 indicating /(?jv7'j; it was used by the Rev. John Michell in 1788, 

 and was adopted by William Smith ; but strictly speaking it was 

 only the name of the Somersetshire quarrymen for the beds of 

 argillaceous limestone in the lower part of the series to which 

 the term Lias is now applied. ^ The Lias is characterized, 

 on the whole, by marked regularity in the strata which compose it ; 

 and these comprise alternations of argillaceous limestone and clay 

 or shale, together with thick beds of marl, clay, and also sand. 



The Lias forms a conspicuous band stretching across England 

 from Whitby and Redcar, on the coast of Yorkshire, to Lyme 

 Regis on the coast of Dorset ; it occupies extensive vales beneath 

 the Oolitic escarpments, while the harder rocks in the Middle and 

 Lower Lias also form escarpments which overlook vales excavated 

 in the softer strata beneath. 



The organic remains of the Lias are rich and varied ; the 

 numerous species of Ammonites and Belemnites, and many other 

 marine Mollusca, are very characteristic, and indicate its essentially 

 marine formation, although the presence of large Saurians and of 

 Plant-remains, as well as the muddy nature of the deposits, suggest 

 the proximity of land, and here and there give more definite 

 evidence of estuarine conditions. Among the Mollusca, Tn'gojiia, 

 Turritella, Liilo?-ma, and Nerita appear, while Carditiia and Hippo- 

 podnirn are confined to the Lias. The remains of Reptiles, particularly 

 of the genera Ichthyosaurus, Phsiosaurus, and Pterodactylus, have 

 led some to designate the period as the Age of Reptiles, or 

 Saurozoic Epoch. Fish, Saurian, and Insect Beds may be 

 recognized at various horizons in the Lias.'^ 



The rapid alternation of limestone and clay in the Lower Lias is 

 remarkable, but may perhaps be partly accounted for by segregation, 

 the hard beds often having a nodular appearance, and frequently 

 occurring in isolated nodular masses. The condition of an embayed 

 sea near a large continent, such as is now seen on the eastern 

 shores of Asia, where rivers, running over extensive flats, pour 

 their waters into a sheltered portion of the ocean, is, in Prof. 

 Ansted's opinion, likely to have characterized the deposition of the 

 Liassic strata. 



The Lias has always been a favourite collecting-ground for those in search of 

 fossils. It is a formation easily recognized, and its fossils, when found, can often 

 be extracted without much difficulty. At the same time the geologist who desires 

 first-rate specimens, must rely largely upon the local collector and dealer. Whitby 



1 De la Beche, Report on the Geology of Cornwall, etc., p. 41. 



~ See The Yorkshire Lias, by R. Tate and J. F. Blake, 1876 ; Martin Simpson, 

 Fossils of the Yorkshire Lias, edit. 2, 18S4 ; J. Phillips, Geol. Oxford, etc., 1871, 

 and Geol. Yorkshire, part i, Coast, edit. 3, 1875 (edited by R. Etheridge) ; E. 

 Witchell, Geology of Stroud, 18S2 ; Wright, Lias Ammonites (Palaeontogr. See). 



