base of the Lias, often crusting the Carboniferous Limestone on which it rests. It is so insignificant in quantity that a few persevering 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 evaporation, between high- and low-water mark. The corals sometimes grew on the Carboniferous Limestone ; and the whole by subsidence 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 Carboniferous Limestone on the land side of the deposit. West of Bridgend, as far as Pyle, the Rhaetic beds become sandstones, indicating 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 France and England, but a scanty representation of the marine life of that period†. As regards the scanty marine life, this is true. Mr. Etheridge, in his paper " On the Rhaetic or Avicula-contorta beds at Garden Cliff "‡, observes that the Rhaetic beds of England and the west and north of Europe, were deposited in shallow seas and in estuaries.
"With Sir Charles Lyell'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 Rhaetic 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 deposition 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, evaporation 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.
† Elements of Geology.
‡ Proceedings of the Cotteswold Naturalists' Field Club, vol. iii. 1865.
