122 Prof. W. H. Miller on Quartz, Ice, and Karstenite. 



doubt that in such a case the water would soon regain its level ; 

 for the ocean at the equator being heavier than at the poles by the 

 weight of a layer 4 feet in thickness, it would sink at the former 

 place and rise at the latter until equilibrium was restored, produ- 

 cing, of course, a very slight displacement of the bottom -waters 

 towards the poles. It will be observed, however, that restoration 

 of level in this case takes place by a simple yielding, as it were, 

 of the entire mass of the ocean without displacement of the mo- 

 lecules of the water over each other to any great extent. In the 

 case of a slope produced by difference of temperature, however, 

 the raised portion of the ocean is not heavier but lighter than 

 the depressed portion, aDd consequently has no tendency to 

 sink. Any movement which the ocean as a mass makes in order 

 to regain equilibrium tends, as we have seen, rather to increase 

 the difference of level than to reduce it. Restoration of level 

 can only be produced by the forces which are in operation in the 

 wedge-shaped mass W C W, constituting the slope itself. But 

 it will be observed by a glance at the figure that, in order to the 

 restoration of level, a large portion of the water W W at the 

 equator will require to flow to C, the pole. 



According to the general vertical oceanic circulation theory, 

 pressure from behind is not one of the forces employed in the 

 production of the flow from the equator to the poles. This is 

 evident ; for there can be no pressure from behind acting on the 

 water if there be no slope existing between the equator and the 

 poles. Dr. Carpenter not only denies the actual existence of a 

 slope, but denies the necessity for its existence. But to deny 

 the existence of a slope is to deny the existence of pressure, and 

 to deny the necessity for a slope is to deny the necessity for 

 pressure. That in Dr. Carpenter's theory the surface-water is 

 supposed to be drawn from the equator to the poles, and not 

 pressed forward by a force from behind, is further evident from 

 the fact that he maintains that the force employed is not vis a 

 iergo but visafronte (Proc. Roy. Geog. Soc. Jan. 9, 1871, § 29). 

 [To be continued.] 



XV. On Quartz, Ice, and Karstenite. By W. H. Miller, 

 M.A., F.R.S., Professor oj Mineralogy in the University of 

 Cambridge*. 



Quartz. 

 MONG the minerals presented to the University by H. "VY. 

 • Elphinstone, Esq., are two crystals of quartz associated 

 with chlorite, apparently from the same, but unknown, locality. 



* Communicated by the Author. 



A 



