250 ANNUAL OF SCIENTIFIC DISCOVERT. 



THE SEA THE GREAT AGENT IN DENUDATION. 



Mr. D. Mackintosh, in a papor on "The Sea a^^ainst Rain and 

 Frost," attempts to show the rehitive power of the two sets of 

 agencies in modifying the surface of the globe. One set of 

 oljservers, at the head of wliioli stands Professor Ramsay, con- 

 siders that the present form of the ground is due to sub-aerial 

 inlluenees; tlie other, led l)y Sir Rodericlv Murcliison, considers 

 tliat tlie sea has been the princiiial denuding or excavating agent. 

 He adduces many facts to jn-ove, 1. That the sea is not simply a 

 levelling agent. 2. Tiiat rain and frost are incapable of produc- 

 ing clids. 3. Tiiat the debris under clilVs is dun to tiie action of 

 the sea. 4. That rain is incapable of abrading hard rocks. 

 5. Tiiat the presence and permanence of glacial markings show 

 the limite<l power of atmosplierii; denudation. He then, in con- 

 clusion, i-eniarks that rain and frost can only justly be regarded 

 as supplementing the denudation eftected by the sea; that their 

 capacity to lower the earth's surface is comparatively small, unless 

 immediately assisted by streams of sufficient transporting power; 

 that the sea, by its laterally excavating agency, and "by uniting 

 in itself at tlie same time and on the same spot a power of detach- 

 ing and removing, can alone prove equivalent to the production 

 of such a series of escarpments, dill's, rocky pillars, terraces, 

 headlands, etc., as those comijrising the more abrupt inequalities 

 of the earth's surface. 



THE ATMOSPHERE AS A DENUDING AGENT. 



Mr. J. B. Jukes and Mr. Scrope ai'e still at issue on this point, 

 the former contending that aqueous atmospheric agencies have 

 most to do with the outline form of the earth, while the latter relies 

 on volcanic influence as the most powerful and most general 

 agency. In a letter, recently published, Mr. Jukes lays down two 

 conclusions which, he says, are in our islands specially ap^^licable 

 to palaeozoic districts, but which, mutatis mutandis, apply to rocks 

 of all ages. They are as follows : 1. The sea has removed vast 

 masses of rock, and left undulating surfaces, the highest points of 

 which ultimately become the summits of mountains. 2. When 

 these undulating surfaces are raised high into the air, they ai'e 

 attacked by atmospheric agencies, and liills, valleys, and plains, 

 are gradually carved out of the rock mass below, their particular 

 features depending on original varieties in the nature of that mass, 

 and variations in the action of the atmosi^heric agencies. The 

 latter depend largely on the variations of temperature, by which 

 water is made to assume the different forms of vapor, water, snow, 

 and ice. It must be recollected that the forms of our palaeozoic 

 grounds are of very ancient date, anterior to the period of the new 

 red sandstone, and that the gi-eat denudation of the older palaeozoic 

 rocks took place even before the deposition of the old red sand- 

 stone. The time, then, during which the atmospheric agencies 

 have been modelling the minor features, is inconceivably great. 

 The recent temporary depression beneath the waters of the glacial 



