The Keuper sandstones and marls contain a great development of chemical deposits, of millet-seed sands, and of many other features pointing to desert conditions, such as sun-cracks, tracks of animals impressed upon a rapidly drying surface, and pseudomorphs of mud after rock salt in the form of cubes and hopper-crystals; furthermore we find the scree-like breccias at different horizons of the Keuper beds where they abut against the old Mendip ridge composed largely of mountain-limestone which furnished the fragments, as was the case with the brockrams abutting against the Pennine ridge. It must be noted that the chemical precipitates of Triassic age consist of the less soluble substances dissolved in ocean water, namely, gypsum and rock salt, whilst the more deliquescent potash and magnesia salts are not represented in Britain. Turning to these continental beds, we get evidence of a general approach to open sea conditions as we pass away from Britain in a south-easterly direction as roughly shewn in the following diagram (fig. 22), where _B_ represents the Bunter beds, _M_ the Muschelkalk, and _K_ the Keuper. [Illustration: Fig. 22.] It will be seen that the mechanical sediments gradually die out and become replaced by calcareous material as one passes from Britain towards Switzerland; the Muschelkalk is very thin in the east of France and thickens out in Germany, while in Switzerland Keuper, Muschelkalk and Bunter are alike largely represented by calcareous deposits, and the mechanical deposits are chiefly argillaceous, the only important sandstone being situated at the extreme base of the Bunter series. The marine development of the Triassic system is naturally the one which is most widely spread, though full appreciation of its importance has only taken place as the result of researches in distant climes of recent years. It is found in southern Europe, in Spitsbergen, in considerable tracts of Asia, including India, and along the Pacific coast region of North America, and everywhere possesses much the same characters. It will be seen from the above remarks that the physical conditions which prevailed in the continental area of Triassic times which is now partly occupied by the British Isles are most closely represented by those of the desert regions of central Asia, hemmed in by the mountain ranges which intercept the vapour-laden winds of the oceans, and cause them to precipitate the great bulk of their vapour on the seaward slopes of the mountains, so that they blow over the deserts as dry winds, causing the fall of any large amount of rain to be a rare though by no means unknown event in the desert regions. _Flora and Fauna of the Period._ The Triassic flora is essentially similar to that of the higher Permian strata, though many of the genera are different.