EDITOR'S TABLE. 



125 



the continued existence of our earth as 

 a place fitted for the hahitation of liv- 

 ing beings, and they must be credited 

 with the total amount of benefit im- 

 plied by the existence and preservation 

 of the life of the globe in all its forms 

 and gradations. We quote enough of 

 the argument of Professor Judd, in his 

 elaborate chapter upon this subject, to 

 substantiate the view here taken : 



"We have had frequent occasion in the pre- 

 ceding pages to refer to the work slow hut 

 sure, silent but effective wrought by the ac- 

 tion of the denuding forces ever operating 

 upon the surface of our globe. The waters 

 condensing from the atmosphere and, falling 

 upon the land in the form of rain, snow, or 

 hail, are charged with small quantities of dis- 

 solved gases, and these waters, penetrating 

 among the rock-masses of which the earth's 

 crust is composed, give rise to various chemi- 

 cal actions of which we have already noticed 

 such remarkable illustrations in studying the 

 ancient volcanic products of our globe. By 

 this action the hardest and most solid rock- 

 masses are reduced to a state of complete dis- 

 integration, certain of their ingredients un- 

 dergoing decomposition, and the cementing 

 materials which hold their particles together 

 being removed in a state of solution. In the 

 higher regions of the atmosphere this work 

 of rock-disintegration proceeds with the great- 

 est rapidity ; for there the chemical action is 

 reenforced by the powerful mechanical action 

 of freezing water. On high mountain-peaks 

 the work of breaking up rock-masses goes on 

 at the most rapid rate, and every craggy pin- 

 nacle is swathed by the heaps of fragments 

 which have fallen from it. The Alpine trav- 

 eler justly dreads the continual fusillade of 

 falling rock-fragments which is kept up by 

 the ever-active power of the frost in these 

 higher regions of the atmosphere ; and fears 

 lest the vibrations of his footsteps should 

 loosen, from their position of precarious rest, 

 the rapidly accumulating piles of detritus. 

 No mountain-peak attains to any very great 

 elevation above the earth's surface, for the 

 higher we rise in the atmosphere the greater 

 is the range of temperature and the more 

 destructive are the effects of the atmospheric 

 water. The moon, which is a much smaller 

 planet than our earth, has mountains of far 

 greater elevation ; but the moon possesses 

 neither an atmosphere nor moisture on its 

 surface, to produce those leveling effects 

 which we see everywhere going on around 

 us upon the earth. 



Tho disintegrated materials, produce 1 by 

 chemical and mechanical actions of the at- 

 mospheric waters upon rock-masses, are by 

 floods, rivers, and glaciers, gradually trans- 

 ported from higher to lower levels ; and soon- 

 er or later every fragment, when it has once 

 been separated from a mountain-top, must 

 reach the ocean, where these materials are 

 accumulated and arranged to form new rocks. 

 Over every part of the earth's surface these 

 three grand operations of the disintegration 

 of old rock-masses, the transport of the mate- 

 rials so produced to lower levels, and the ac- 

 cumulation of these materials to form new 

 rocks, are continually going on. It is by the 

 varied action of these denuding agents upon 

 rocks of unequal hardness, occupying differ- 

 ent positions in relation to one another, that 

 all the external features of hills, and plains, 

 and mountains owe then - origin. 



It is a fact, which is capable of mathemati- 

 cal demonstration, that by the action of these 

 denuding forces the surface of all the lands of 

 the globe is being gradually but surely low- 

 ered ; and this takes place at such a rate that 

 in a few millions of years the whole of the 

 existing continents must be washed away and 

 their materials distributed over the beds of 

 the oceans. 



It is evident that there exists some agency 

 by which this leveling action of the denuding 

 forces of the globe is compensated ; and a lit- 

 tle consideration will show that such com- 

 pensating agency is found in the subterra- 

 nean forces ever at w r ork within the earth's 

 crust. The effects of these subterranean 

 forces which most powerfully arrest our at- 

 tention are volcanic outbursts and earthquake- 

 shocks, but a careful study of the subject 

 proves that these are by no means the most 

 important of the results of the action of such 

 forces. Exact observation has proved that 

 almost every part of the earth's surface is 

 either rising or falling, and the striking and 

 destructive phenomena of volcanoes and 

 earthquakes probably bear only the same re- 

 lation to those grand and useful actions of the 

 subterranean forces which floods do to the 

 system of circulating waters and hurricanes 

 to the system of moving air-currents. . . . 



We establish the fact of the movement of 

 portions of the earth's crust by noticing the 

 changing positions of parts of the earth's sur- 

 face in relation to the constant level of the 

 ocean. When this is done we find abundant 

 proof that, while some parts of the earth's 

 crust are rising, others are as undoubtedly 

 undergoing depression. 



"We shall be able to form some idea of the 

 vastness of the effects produced by the sub- 



