110 G. H. Kinahan — On Denudation. 



action to Suhcerial (Chemico-fluvial), as these two forces work so dif- 

 ferently. A glacier has been said to belong to the chemico-fluvial 

 agencies, as "it is only a frozen river:" but compare the work 

 a glacier and its tributaries can do with that of a river and its 

 tributaries. The tributaries of the first are beds of snow and ice, 

 while those of the latter are all the chemico-fluvial forces com- 

 bined ; the glacier and its tributaries works altogether by mechani- 

 cal action, being confined to planing and triturating rock, except 

 when it does a little quarrying by tearing off masses of rock ; while 

 the chemico-fluvial denudation is due to chemical and mechanical 

 action combined, moreover, the latter is quite different to that 

 exercised by ice, for it is principally carrying away materials 

 loosened by chemical action ; the only trituration it accomplishes 

 being that done in river-rapids and mountain torrents ; but it does 

 not appear capable of planing down a rock ; and ice, as icebergs, may 

 possibly be able to denude the sea bottom on which none of the 

 other forces can act. Many rocks, such as dolerite, diorite, diabase, 

 granite, some limestones, etc., are physically hard, while they are 

 chemically soft ; others, such as slates, schists, clays, etc., are phy- 

 sically soft while they are very little susceptible of chemical decom- 

 position. The former, therefore, are easily denuded by the chemico- 

 fluvial agents, and the latter resist them ; also while a planing action, 

 such as that exercised by ice, would be resisted by physically hard 

 rocks, it could easily excavate and cut away the soft ones ; and are not 

 these the results found in nature ? In an ice — " dressed, planed, and 

 and etched" — country, all the physically hard rocks have formed 

 features from a few feet in height to hundreds or more ; but since 

 the ice has disappeared the chemical agencies have had their sway, 

 and these rocks are now weathering fast ; while the chemically hard 

 but physically soft rocks — those that under the old regime suffered 

 most — are now almost perfectly immolested. 



It has been stated " that glaciers can do very little work in exca- 

 vating their valleys." This may, possibly, be the case ; but if we 

 look at the rivers always flowing from them — ever turbid and white 

 with the silt formed by the trituration of the blocks and fragments of 

 rock in the ice grinding against one another, and the sides and bottoms 

 of the valleys — we may be excused for not putting implicit faith in 

 the assertion.^ Moreover, this work is never ending from one year's 

 beginning to another year's beginning, as long as the glacier lasts ; 

 while fluvial action only exists in full force during part of the year ; 

 however, it must be allowed its accomplice, chemical action, is 

 always at work. 



The chemico-fluvial agents are undoubtedly the most universal 

 performers in the great work of denudation, as they are aiixiliaries to 

 the other two, and, when combined, the work done is enormous ; but 

 individvially no one force seemingly can do much work. With the 

 glacier they combine, in the shape of wind, frost, etc., and quarry 



1 Hayes says "The ice was perfectly pure and transparent" (of " Tyndall 

 glacier"), " and yet out of its very heart Avas pouring the muddy stream of which 

 1 have made mention." — "The Open Polar Sea." p. 436. 



