384 PREHISTORIC E UR OPE. 



indeed, a considerable valley opens more or less directly upon 

 the sea, we find the lower reaches of its river almost invariably 

 flowing through tracts of flat country, the upper surface of which 

 may reach from 5 or 10 to 20 or 30 feet above the level of the 

 sea. These flats, however, when they are followed inland begin 

 in a shorter or longer distance from the sea-coast to rise with a 

 more or less gentle gradient, and so pass gradually into what we 

 at once recognise as old terraces of fluviatile formation. Along 

 the margins of the open sea the raised-beaches are generally 

 narrow, and this is most markedly the case where the coast is 

 more or less abrupt. Thus, in many places, the sea is bordered 

 by a mere narrow strip of flat ground not exceeding a hundred 

 yards in breadth, and abutting abruptly against rock-cliffs, the 

 under portions of which often show old sea -worn caves and 

 gullies. In other districts, again, where the land descends 

 with a gentle gradient to the shore, the raised-beaches some- 

 times attain a width of one or two miles or even more. 



The organic remains occurring in these beaches and estuarine 

 flats consist of the common forms that are still indigenous to our 

 coasts, such as cockle, mussel, oyster, periwinkle, Scrdbicularia 

 piperata, Hydrobia ulvce, Tellina balthica, etc. The presence of 

 the large Greenland whale, however, remains of which have been 

 met with in the great estuarine flats of the Forth, is not without 

 its significance, and may possibly point to a somewhat colder 

 sea than the present. But on the other hand we find on the 

 borders of the Firth of Clyde a postglacial accumulation of shells, 

 some of which seem to bespeak milder conditions of climate than 

 the present. Mr. Crosskey has drawn special attention to this 

 deposit. " It contains such shells," he says, "as Psammobia fer- 

 roensis and Tellina incarnata {tenuis ?), of larger size and in 

 greater numbers than they at present occur living in the neigh- 

 bouring seas," a fact indicating, he thinks, conditions of climate 

 possibly more genial than those which exist at the present day. 



The postglacial deposits of Scotland frequently rest directly 

 upon glacial accumulations, and between the two series there 

 is unquestionably a " break." We find no " passage-beds " be- 



