UPON ROCKS OF THE NEAV YORK SYSTEM. 431 



Throughout all the strata thus marked, there are no ripple- 

 marks ; though, in strata above and below this point, they ai-e 

 common, and within ten feet of the strata marked by wave lines 

 I have seen rippled surfaces. 



Notwithstanding, it is evident that this portion of the strata re- 

 mained above water, or so that it was washed by the retiring tide 

 for some length of time ; yet it is equally evident, that it did not 

 become permanently dry land. It appears more like a sand- 

 bar, or elevated portion of tlie ocean bed, which might have been 

 dry a part of the time. It should be mentioned at the same time, 

 that this portion of the rock, thus marked, is a gray quartzose 

 sandstone, while both below and above, the mass is a red shaly 

 sandstone. The gray color does not appear due to any subsequent 

 action, but to have been that of the deposit. The great horizontal 

 extent of the mass forbids the idea, that it was due to a sudden 

 or local phenomenon, for the numerous thin laminae, of which it 

 is composed, indicate a considerable period of time. It is further 

 remarkable, that during this period there was an entire cessation 

 of the shaly deposit, which occurs just above and below, and the 

 coloring matter also, for the most pai't, ceased during the same 

 time. (N. York Geol. Report, 4th Dist., Art. Medina Sandstone.) 

 In view of the facts first stated, if they are admitted to be sub- 

 stantiated, we must conclude, that denuding agencies have ope- 

 rated at remote periods of the earth's history, not only between 

 great geological eras, but during the deposition of products, 

 which form one system. The absence, in some places, of 

 masses, which in others constitute important rocks, seems often 

 to point to a cause of their absence in removal after deposition, 

 rather than to thinning out from want of matter, or being beyond 

 the reach of the transporting power. We have, in the case of the 

 Oriskany sandstone in New York, an example of this kind, where 

 the mass does not apparently thin gradually, but terminates 

 abruptly, and appears beyond this point in patches, as if it had 

 formed outliers previous to the deposition of the superincumbent 

 masses. The evidence of its destruction is not only indicated m 

 this way, but by the presence of rounded masses, forming peb- 

 bles upon its surface, and imbedded in the succeeding rock. 



