'I'll 1C TKIAS8IC SYSTEM 377 



ka which liere crosses the valley of the Rhone between that 

 jil.io- and Valence, and it is probable that this was part of the 

 barrier which separated the northern and southern basins of depoei- 

 timis. South of Valence similar deposits set in again and form a 

 long strip by Privas and Largentiere, and again in the Lode've 

 ili-trict; they also occur in the Pyrenees and in Eastern Spain, but 

 to tind a complete Triassic Series one must go to the Maritime Alps, 

 \v licic lower beds come in and the series expands eastward into 

 the Apennine facies which is similar to that of the Eastern Alps. 



The only other Triassic tract in France which need be 

 noticed is that in Normandy, occupying a bay-like depression in 

 the Arcluean rocks from Valogne and St. Waast on the north 

 to St. Lo and Littry on the south, but thinning out to the west 

 of Caen. The beds consist of gravel and conglomerate at the base, 

 ]>;i ing up into a doloinitic conglomerate which is succeeded by 

 red sandstones and marls. The maximum thickness is not more 

 than 200 feet, and the whole is probably of Keuper age, the beds 

 being shore deposits, like those round the Mendip and Quantock 

 Hills in England. 



E. THE HISTORY OF THE EUROPEAN TRIAS 



From the preceding descriptions of the Triassic strata which 

 are found in different parts of Europe the student will have 

 gathered that considerable geographic changes took place during 

 tin- course of the period ; though these seem to have been accom- 

 plished slowly and without the forcible uplift of any mountain 

 chain like that of the Armorican ranges in Carboniferous time. 



The change from Permian to Triassic conditions seems to liave 

 been effected by a slow upheaval of the whole of Northern Europe, 

 so that all those parts of the Permian Sea which lay within that 

 region were shallowed and some portions of them were converted 

 into sandy plains. This seems especially to have been the case in 

 the British area where the north-west gulf of the Permian Sea 

 became a sandy desert, swept by winds which probably blew 

 chiefly from the north, like those which blow over Persia and 

 Beluchistan at the present day at certain times of the year. 



Through this plain may have meandered a river fed by the 

 streams which flowed off the western and northern mountains, so 

 that it was a strong and rapid river even though it may have 

 received no affluent after leaving the gap between Ireland and 

 Scotland. Such is the theory by which the accumulation of the 

 "Pebble Beds" in the English Midlands has been explained, for 

 the majority of these pebbles are quartzites which are unlike any 



