RAMBLES OF A GEOLOGIST. 321 



swept by a streamlet After every shower, the stream comes 

 down red and turbid with the finer and more argillaceous 

 portions of the deposit ; minute accumulations of sand are 

 swept to the gorge of the ravine, or cast down in ripple 

 marked patches in its deeper pools ; beds of pebbles and gravel 

 are heaped up in every inflection of its banks ; and boulders 

 are laid bare along its sides. Now, a separation, by a sort 

 of washing process of an analogous character, must have taken 

 place in the materials of the more exposed portions of the 

 boulder-clay, during the gradual emergence of the land ; and 

 hence, apparently, those extensive beds of sand and gravel 

 which in so many parts of the kingdom exist, in relation to 

 the clay, as a superior or upper subsoil ; hence, too, occasional 

 beds of a purer clay than that beneath, divested of a consi- 

 derable portion of its arenaceous components, and of almost 

 all its pebbles and boulders. This washed clay, a re-forma- 

 tion of the boulder deposit, cast down, mostly in insulated, 

 beds in quiet localities, where the absence of currents suffer- 

 ed the purer particles held in suspension by the water to 

 settle, forms, in Scotland at least, with, of course, the ex- 

 ception of the ancient fire-clays of the Coal Measures, the 

 true brick and tile clays of the agriculturist and architect 



It is to these superior beds that all the recent shells yet 

 found above the existing sea-level in Scotland, from the Dor- 

 noch Frith and beyond it, to beyond the Frith of Forth, seem 

 to belong. Their period is much less remote than that of 

 the shells of the boulder-clay, and they rarely occur in the 

 same comminuted condition. They existed, it would appear, 

 not during the chill twilight period, when the land was in a 

 state of subsidence, but during the after period of cheerful 

 dawn, when hill-top after hill-top was emerging from the deep, 

 and the close of each passing century witnessed a broader area 

 of dry land in what is now Scotland, than the close of the 

 century which had gone before. Scandinavia is similarly 



x 



