BY HUGH MILLEE. 305 



may be reckoned as nothing."* Ey rain, as distinguished from 

 rivers, however, must be held to be included in this aspect those 

 invisible trickling runnels that form the capillaries of the sys- 

 tem of water-circulation; and true as Col. Greenwood's dictum 

 may, in a measure, be of mechanical waste, it is much more ap- 

 plicable to chemical. It is while quietly wetting rocks and lying- 

 hid among vegetation that water mainly applies the carbonic acid 

 which it sucks from the air and from decaying plants, to the de- 

 composition of their carbonates and silicates. 



To the general rule that work so unobtrusive as that accomp- 

 lished by rain is measured only by general results there is a 

 remarkable exception — familiar enough, perhaps, but worth re- 

 calling. On the slope of a bank of clay little semi-detached 

 pillars may sometimes be noticed, each capped by a pebble, which 

 by warding off the rain from the clay beneath it, has preserved 

 a tiny monument of the rain-wash around. In valleys of the 

 Tyrol, in this manner, forests of large columns of indurated clay, 

 each capped by its protecting stone, some as much as a hundred 

 feet high, have slowly become developed ; the rainfall of every 

 few years working noticeable changes among them.f I observed 

 lately, in some excavations, a number of detached pillars of 

 clay left standing by the quarrymen, and inquired the reason. 

 ''These," I was answered, ''mark piecework." The Tyrol 

 earth-pillars mark, in a very imperfect degree, geological piece- 

 work ; and Eain was the quarrier ; but very seldom is there any 

 measure for its work. The great breadth of many of our own 

 valleys is in large part the result of the imperceptible action 

 of these silent forces. 



To rain, as an assistant, may be added Wind. No one who 

 has heard blasts hurtling among the rifts of a crag should over- 

 look wind as a co-operator with rain in bearing away loosened 

 particles of rock. Whilst climbing the steep sides of one of the 

 grand natural pyramids of North -"West Scotland — Coulmore, 

 Assynt, I was assured by an intelligent shepherd that he had 

 seen a slab of rock of more than a hundredweight lifted up bodily 

 by a sudden gust; and having had personal experience only a 



* Op. Clt., p. 189. t Lyeir» Principles of Geology, 12tli Ed., Vol. I., p. .129. 



