Geology and Physical Geography. 333 



entire thickness of the deposit are also scratched and polished, 

 that it was not before, but at the time ; seeing that the pro- 

 cess of scratching and polishing went on during the entire 

 period of the formation, beginning with its lowest layers, and 

 not terminating until its uppermost were cast down. The 

 dressed surfaces and the boulder clay are contemporary 

 phenomena. The smaller stones must have been fastened 

 ere they could have been scratched. Even, however, if the 

 force of water could have scratched and furrowed them, it 

 would not have scratched and furrowed them longitudinally, 

 but across. Simple water could not have been the agent 

 here ; nor yet an eruption of mud propelled along the surface 

 by some wave of translation produced by the sudden upheaval 

 of the bottom or shore of the sea. When a large raft of 

 wood, floated down a river, grates heavily over some shallow 

 bank of gravel and pebbles resting on the rock beneath, it 

 communicates motion, not of the rolling, but of the launch- 

 ing character, ta the flatter stones with which it comes in 

 contact. It slides ponderously over them ; and they, with a 

 speed diminished in ratio from that of the moving power, in 

 proportion to the degree of friction below or around, slide 

 over the stones or rocks immediately beneath ; and thus, to 

 borrow my terminology from our Scotch law courts, they are 

 converted at once into scratchers and scratchees. For rafts 

 of wood we have but to substitute rafts of ice, a submerged 

 land, covered by many fathoms of sea, for the shallows of the 

 river, and some powerful ocean-current, such as the Gulf or 

 Arctic Stream, for the river itself, as we at once arrive at a 

 theory of the boulder clay and its origin, which seems to 

 account more satisfactorily for the various phenomena of the 

 deposit than any of the others. 



Mr Maclaren described certain ridges and mounds of soil 

 in Glenmessan (Argyleshire), which bore a resemblance to 

 the moraines of glaciers. They rise abruptly from the bottom 

 of the valley, are composed of materials similar to those of 

 moraines, consisting of confused piles of gravel, clay, and 

 blocks of stone, and they occupy similar positions. The rocks 

 forming the sides of the valley are also smoothed to a great 

 height, and exhibit well ^marked strise and groovings. He 



