CONCLUSIONS. 165 



rotation or movement about a fulcrum line in relation to the shore, but 

 also the form of the bottom of the deeper seas, the water-displacing value 

 of other lands in their several movements of up-and-down going, the at- 

 traction of ice-caps, wliich rapidly vary in importance, that of mountains 

 and other high-lying lands, which varies in a less rapid way, as well as 

 other intiuences wliicli have not been taken into account. It may be 

 noted in passing that no reckoning has been made as to the progressive 

 effect arising from the importation of sediments into the sea. The phe- 

 nomena whicli are associated with this action are too complicated for 

 discussion in this paper, where limitations as to length must be consid- 

 ered. It seems well, however, to advert to them. 



So far we have not succeeded in obtaining data which will enable us 

 to determine, even in an approximative way, the amount of detritus an- 

 nually contributed to the bottom of the sea and there built into clastic 

 rocks ; yet we perceive that, in addition to the contribution from the 

 lands borne in by the atmospheric agents and the waves and tides, there 

 is probably a yet vaster amount contributed to the floor of the deep by 

 volcanic ejections. As there is probably not more than about 10 per 

 cent of the detrital accumulations which is occupied ])y the fluid, the 

 eflect of the deposition, excej^t so far as it is compensated by the move- 

 ments of the sea-bottom and the land masses, is to lift the plane of the 

 oceanic waters in what may l)e termed a geologically rapid manner. 

 This will be seen ))y a consideration of the following facts : The average 

 downwearing of the land — that is, the rate of exportation of its mate- 

 rials to the sea-floor — is probal)ly at least as rapid, taking into account 

 both atmospheric and seashore actions, as 1 foot in 8,000 yards. The 

 inquiries of various naturalists concerning the Javanese volcanoes ap- 

 pear to indicate that 100 cul)ic miles or more of detrital matter has l)een 

 poured forth from these vents during the last hundred years, practically 

 all of wliicli has found its way to the sea-floor. The total amount of 

 this contribution of sediments to the oceans from this small but very 

 active group of volcanoes during the time mentioned })robably exceeds 

 the supply afforded by all the rivers of North and Soutli America. 



It thus appears to me evident tliat the water-displacing value of the 

 marine sediments accumulated in the course of a million of years miglit, 

 if other sources of change were excluded, suffice to affect the general sea- 

 level to the amount of some score or perhaps hundreds of feet. Owing, 

 however, to the other sources of instability of the land, this influence is 

 perhaps of small value in the c<juation which determines the position of 

 a shoreline. 



Although I do not regard the facts above noted, wliich ai>{)ear to show 

 the prevailing low position of the coastlines of the world, as of decisive 



X-Xni— Bill. r;roL. So<.. Am., V.ji.. r,, iHOt. 



