304 TYNEDALE ESCARPMENTS ; 



constituents ; the other to move them when loose to the nearest 

 stream. Such factors are Frost and Rain. 



1. Frost. — Being the servant of larger forces, frost was not 

 named in our general review of denudants. "^Tien showers of 

 rain have saturated rocks, soaking into their pores, and filling 

 their cracks and joints, a sudden change of temperature often 

 comes to seal the moisture up into ice. The expansion that accom- 

 panies the process of freezing takes place with prodigious force. 

 A very small wine-glassful of water tightly plugged into a bottle 

 of cast-iron half an inch thick is enough to burst it ; and in like 

 manner each fi-ost that may be seen ornamenting the face of some 

 of these crags with glistening points and little colonnades, has set 

 agoing within it a vast amount of disparting energy, expended 

 both in sundering en masse and in separating grain from grain. 

 And what so affects harder rocks does not fail to swell up and 

 loosen the softer, as is familiar upon a roadway after a thaw. 

 Yogotation is an important assistant to frost by lodging moisture 

 and keeping it in contact with suiiaccs of rock. 



2. Rain and Wind. — AVhen pulverized or loosened the mate- 

 rials are ready for transport by Rain. Every drop of a heavy 

 shower that beats on the soil of a hill side shifts a few particles 

 one little stage downhill. It was the advice of one well fitted to 

 be an adviser on such subjects, that "if your neighbour's land 

 lies below you on a steep hill side, unless you wish to make 

 him a present of your soil, pound it back on to your own land 

 by a fence, and when it accumulates against your own fence cart 

 it uphill again."* But though the travelling of loose soil is 

 familiar to all culturers of hilly ground, it is impossible to mea- 

 sure the " portage" actually accompli.shed in tliis way. Streams, 

 as being the first ^'i8ible index to the transporting processes, are 

 apt to get an amount of credit not justly their duo. Yet no one 

 has contradicted, so far as 1 know, the assertion of the late Col. 

 Greenwood, than whom there could be no more diligent student 

 of "Rain and Rivers," that "in comparison to the broad waste 

 from the waali of ruin, tlie waste by the direct action of rivers 



• Col. ar«enwou(l'* Troeltrtcr, 2ncl Edition, 18fi.«». 



