On some points in Mallet's Theory of Vulcanicity . 41 



ocean-level as a datum plane, the changes of level originating 

 land and sea may have tended rather to accelerate than retard 

 the earth's rotation. Taking the mean of the sediment stated 

 to be carried by six great rivers, namely the Mississippi, Po, 

 Vistula, Rhine, Ganges, and Rhone, it amounts to about ywo" 

 in volume of the water discharged ; and if we apply this to the 

 water discharged from the whole surface of the land, as above 

 stated, we have ^ r ^^ J L =19 , 90 cubic miles of sediment annually 

 discharged at the sea-level. These rough estimates are pro- 

 bably far from correct, and we do not know with any pre- 

 cision what is the mean specific gravity of this sediment, nor 

 from what mean height it may be considered to have descended ; 

 but we can easily see that the loss of rotative energy during the 

 descent of this vast mass, if transferred to the globe as a whole, 

 is scarcely negligible. Nor does this represent all that we have 

 to deal with. The sediment finally carried into the sea repre- 

 sents the real annual degradation of the land by rain and rivers; 

 and the huge block that falls to-day from a Sierra summit and 

 wedges itself a few miles off immovably in the cleft of a canon, 

 though it may not reach the sea for thousands of years, during 

 which it is slowly transformed into sediment, is nevertheless 

 effective, as is the ice which thaws or falls in avalanche, in trans- 

 ferring to our earth the energy of rotation they lose in descent. 

 Whether or not it be true that, viewed on its largest scale and 

 at some indefinitely remote period yet to come, the movements 

 of all the bodies of the universe tend to ultimate rest, and an 

 end of the present order of things, it seems a fact that all the 

 smaller perturbations of planetary movement at least, as for 

 example those of precession and nutation, are involved in con- 

 ditions which prevent their passing a certain limit, and which in 

 other cases equilibrate the disturbing cause. It would seem, 

 therefore, contrary to analogy to suppose the case of the retar- 

 dation of our globe by tidal friction, whatever may be its actual 

 amount, to be an exception and to go on unchecked, until the 

 astronomical consequences pointed out by Thomson and others 

 shall have occurred in the motions of our satellite, our earth, 

 and the sun. 



VI. On some points in Mallet's Theory of Vulcanicity. 

 By Eug. W. Hiigard, University of Michigan*. 



^^HE main points of Mallet's Theory of Vulcanicity have 

 been before the world of science for some time, and have 

 excited some lively discussions on both sides of the question, 



* From Silliman's American Journal, June ]$74. 



