186 ME. A. RENDLE SHORT ON RHJETIC [May I904, 



becoming extremely saline, like the Dead Sea to-day. He remarked 

 {op. cit. p. 196):— 



' The thin Rhtetic beds of North -Western Europe might have been deposited 

 in great part in shallow seas and in estuaries, or in lagoons, or in occasional 

 salt-lakes of small or great dimensions, separated from the sea by accidental 

 changes in physical geography.' 



Moore (13) referred to the Rhastics as oceanic, and Etheridge spoke 

 of Penarth as being in the middle of the Rhastic ocean (17). 



Some writers, following a suggestion by Brodie (1), have con- 

 sidered that the Rhastic Series is estuarine. jNow it is, I think, 

 generally admitted that Ramsay's theory of the Keuper is correct. 

 There was a vast lake covering a large part of England, which 

 gradually evaporated. The conditions were probably desertic. 

 Therefore over that area there would be a more or less uniformly- 

 horizontal surface, with perhaps very gently-shelving shores, and 

 occasional deeper pools and channels. The Triassic lake seems to 

 have evaporated nearly to dryness, except in the pools and channels 

 which were a few feet deeper. The evidence of this is to be found 

 in the minerals — rock-salt, for instance, indicating great concen- 

 tration — and in the footprints on the Keuper shores. 



Thus, before the Rhastic sea entered, the conditions were as 

 favourable as could be for the deposition of very shallow-water beds 

 over a very wide area. When matters stood thus, a gradual de- 

 pression of the land allowed the Rhastic sea from Germany and 

 Prance to enter, very gently at first. The channels that it more par- 

 ticularly entered were freshened, and the Rhastic Series of the infra- 

 Bone-Bed horizon at Watchet, etc. was laid down, while Black Shales 

 commenced to form in various places. Then came the storms which 

 produced the Bone-Bed, and swept the waters over the just uncovered 

 flats. Probably this storm also broke up the dry weather, and 

 ushered in a wetter season. Owing to this, and to continuance of the 

 slight depression, nearly the whole area of the old Keuper lake was 

 covered by the shallow Rhastic sea. Although most of the Rhastic 

 has now been removed by denudation, it is nearly always found 

 where any beds resting upon the Trias have been left; and that not 

 only along the Jurassic escarpment, but also at Watchet, Penarth, 

 and near Burton-on-Trent (16). The chief exception is in part of 

 Lincolnshire, where the Rhastic and Planoi'bis-zones are said to be 

 absent (21). Throughout the whole Rhastic Period, the same con- 

 ditions of extensive very shallow-water conditions, over the entire 

 Triassic lake, prevailed. There was, of course, communication with 

 the Alpine and Germanic Ocean to the south. Owing to the pauses 

 in depression, the sea was in most places nearly silted-up by the 

 time when the Naiadita-Beds were laid down, and every evidence of 

 shallow water, and occasional exposure to the air, over wide areas, 

 has been preserved. The ripple-marks, sun-cracks, and insect-wings, 

 the paucity of big saurians between the Bone-Bed (which was laid 

 down by a storm such as still washes whales into shallow water and 

 breaks them up) and the White Lias — all these tell the same tale. 



Slight depression then again occurred, and clays were laid down. 

 Once again the depression was balanced by silting-up, and the 



