I.—On the Evidence for Desert Conditions in the British Trias

Abstract

A paper by Mr. J. Lomas on “Desert Conditions and the Origin of the British Trias” appeared last year in the Proceedings of the Livepool Geological Society, and was reprinted, with some slight abridgement, in the November and December numbers of this Magazine. Valuable and suggestive as it is, I venture to think that its author, as is not unfrequent with enthusiastic advocates, is attempting to prove too much. I have more than once expressed my belief that the pebble beds of the Bunter, perhaps also its Upper and Lower Sandstones, were deposited on a lowland by mountain-fed rivers, and think it very probable that this lowland, in consequence of its temperature rather extreme, as is the case in Turkestan and parts of Persia; the occasional wind-worn sands being due to the one cause and the angular breccias to the other. But I think the Keuper Marls, on the whole, aqueous rather than æolian in origin, and the Lower Keuper Sandstones, with the Waterstones, indicative of the gradual setting in of inland sea conditions. From time to time, before the salt lake attained its greatest dimensions, the wind might blow the lowland dust into dunes or carry it away from the shore till much of it settled down beneath the water, but I still think that a large part of the material, which now forms the red marl, was brought down as river mud to this magnified Dead Sea, by the streams which had formerly transported sand and pebbles. In regard to this, however, we cannot at present speak dogmatically. More study is needed of the constituents of the Keuper Marl, of fluviatile, lacustrine, and even marine muds, as well as of the lighter æolian deposits, before we can determine what parts wind and water have respectively taken in making this member of the Trias. Here, however, I may remark that neither Professor Watts nor Mr. Walcot Gibson was the first to observe that in the Charnwood Forest region the Keuper fills up hollows in the older rocks.