646 STKATIGRAPHICAL GEOLOGY 



trees are frequently intercalated with the silts, and mark pauses in 

 the process of silting up. Many such tracts pass beneath the 

 present beaches, and were evidently once much more extensive 

 than they are now. Such are the marshes near Fleetwood, in 

 Lancashire, the Bridgewater Levels in Somerset which pass 

 beneath the Bristol Channel and must formerly have extended 

 far down this estuary, the Pevensy Levels in Sussex, the Romney 

 marshes in Kent, the Fens of Cambridge and Lincoln, and the 

 marshes of the East Lincolnshire coast. 



3. Continental Deposits 



The cave earths and river deposits of France and other con- 

 tinental countries do not differ in any essential respect from those 

 above described, and the French classification of them according to 

 types of flint implements lias already been mentioned (p. 638). 

 Here, therefore, it is only necessary to describe such deposits as differ 

 from anything existing in Britain. Of these the two chief are 

 (1) the Loess, (2) the post-Glacial deposits of the Baltic area. 



The Loess. This deposit is found in the north-east of 

 France, and in the valley of the Rhine as far south as Basle, over 

 parts of Southern Germany, the lower parts of Bohemia, Moravia, 

 Hungary, and Galicia, up into the Carpathian Mountains, and also 

 through Poland and Silesia over the plains of Southern Russia. 

 Though thickest in the valleys, it also extends onto the slopes of 

 the hills and reaches up to levels of 2000 and even 3000 feet, but 

 is there mingled with local detritus. 



Loess is a fine yellowish or brownish argillaceous material, 

 similar to some of the yellow loams which occur in fluviatile 

 deposits, but it is unstratified and has a marked tendency to break 

 along vertical planes and thus to form vertical walls. It is 

 always more or less calcareous, and often contains calcareous concre- 

 tions, but the upper part is generally decalcified. It appears to 

 be a terrestrial deposit, for the fossils it contains are almost entirely 

 land-shells and mammalian bones ; freshwater shells being of rare 

 occurrence. The commonest shells are Helix (Hygromia) hispida, 

 Succinea oblonga, and Pupa muscorum. 



Diverse views have been held with regard to the origin and the 

 age of the loess ; some have thought that it resulted from the 

 blocking of the great rivers flowing from Central Europe, their 

 waters being ponded back by the northern ice-sheet and large 

 lakes thus formed. Others with more reason regard it as an 

 aeolian deposit formed during an epoch of dry cold ; that it was, in 

 fact, an accumulation of dust carried by the wind and deposited on 

 grassy steppes like thbse of Southern Siberia. This has been 



