1871.] BAMSAT LOWER LIAS. 195 



base of the Lias, often crusting the Carboniferous Limestone on 

 which it rests. It is so insignificant in quantity that a few perse- 

 vering palaeontologists might almost carry it away bodily in their 

 bags ; and its manner of occurrence has always suggested to me 

 the idea that it was formed in hollows in the rocks, partly by eva- 

 poration, between high- and low-water mark. The corals some- 

 times grew on the Carboniferous Limestone ; and the whole by sub- 

 sidence was afterwards buried underneath the Lias. Mr. Bristow 

 remarks that this mode of formation explains the presence of galena 

 and chert in the tufa*. They have been derived from the Car- 

 boniferous Limestone on the land side of the deposit. West of 

 Bridgend, as far as Pyle, the Ehsetic beds become sandstones, indi- 

 cating an approximation towards the margin and shallow water. 



Sir Charles Lyell has remarked that "the sandstones and clay 

 of the Keuper resemble the deposits of estuaries and a shallow sea 

 near the land, and afford in the north-west of Germany, as in Prance 

 and England, but a scanty representation of the marine Ufe of that 

 periodf . As regards the scanty marine life, this is true. Mr. 

 Etheridge, in his paper " On the Rhsetic or Avicula-contorta beds at 

 Garden Cliff "J, observes that the Ehsetie beds of England and the 

 west and north of Europe, were deposited in shallow seas and in 

 estuaries. 



With Sir Charles Ly ell's suggestion, as regards the estuarine 

 nature of the Keuper beds of England, I do not agree, while Mr. 

 Etheridge seems to me to be right respecting the conditions under 

 which our Ehaetic beds were formed. My reasons for this opinion are 

 chiefly founded on physical considerations, leading to the following 

 conclusions, which form the main object of this paper. 



1. The Triassic epoch over a great part of what is now Europe was 

 essentially a terrestrial one ; that is to say, the Trias areas of depo- 

 sition in part, and some of them altogether, were surrounded by 

 continental land. In the latter part of this epoch the Keuper marls 

 were deposited in the British isles in a great lake, fresh or brackish 

 at the beginning ; and the same was occasionally true of other areas 

 of northern Europe and its adjoining seas, which lakes were for the 

 most part destitute of outlets to the sea. 



2. These lakes gradually got filled with sediments. By and by, 

 through change of amount of rainfall, or through increase of heat, 

 the lake or lakes ceased to have an outflow ; that is to say, evapora- 

 tion was equal to, or greater than, the influx of water. 



3. By degrees, through evaporation, the water became Salter; 

 concentration of salt or salts in solution ensued ; and precipitation 

 of rock salt was one of the results. 



* I have examined the Sutton beds with Mr. Bristow, and have no doubt 

 that they are Lower Lias. See " On the Lower Lias or Lias- Conglomerate of a 

 part of Glamorganshire," Bristow, Quart. Journ. Geol. Soc. 1867, vol. xxiii. 

 p. 199. See also Mr. Charles Moore, " On Abnormal Conditions of Secondary 

 Deposits," Quart. Journ. Geol. Soc. 1867, vol. xxiii. p. 526. Mr. Moore decides 

 the Sutton beds to be of Lower Liassic age. 



t Elements of Geology. 



X Proceedings of the Cotteswold Naturalists' Field Club, vol. iii. 1865, 



