744 JOURNAL OF GEOLOGY. 



and Mr. Russell, some years ago, espoused the idea that their present 

 surface was a comparatively small part of their original basins. This 

 matter is essentially indeterminate at present ; but the valid evidence 

 of great post-Newark erosion disposes me to accept almost any measure 

 of former extension of the system that may be required by reasonable 

 argument. At first, the mind halts before the supposition that vast 

 masses have been uplifted and worn away in the ages since the date of 

 the Newark deposition, but the evidence of vast denudation in that 

 interval is now so complete that it no longer seems warrantable to 

 withhold belief in the "broad terrane hypothesis," either from its 

 extravagant erosion of rock masses, or from an apparent insufficiency 

 of time for such extravagance. 



On the other hand, while it seems likely that there was some con- 

 nection between the several separate Newark areas, because their fauna 

 and flora are so similar, it does not seem necessary to conclude that all the 

 space between the Connecticut and the New Jersey areas was once over- 

 spread by Newark strata. It may have been. There was time enough 

 during the Newark deposition to furnish material for such a cover ; 

 and there has been time enough since then to wear it away ; but still 

 there is no direct evidence that it existed. The original boundaries 

 of the formation are very vaguely defined. 



Noticing that a greater definiteness of results has been gained in 

 the Connecticut valley than in the other Newark areas, it is evident 

 that the physical conditions of origin of the trap sheets in the south- 

 ern areas deserve the closest scrutiny. If they prove to be intrusive 

 sheets, they are of little structural value. But if they are proved to be 

 extrusive, they may then be treated as conformable members of the 

 stratified series, and thus a key to the general attitude of the system is 

 gained. After this step, the detection of sequences of strata, includ- 

 ing extrusive trap sheets with the aqueous sediments, is of next import- 

 ance, as by this means faults may be located, and thus some advance 

 made in the general reconstruction of the formation. 



But even where best studied out, it is likely that the cross sections 

 by which underground structure is represented are hardly more than 

 parodies on the facts ; so insufficient are the opportunities for the dis- 

 covery of deep internal structures. A close knowledge of the system 

 seems beyond reasonable expectation. 



W. M. Davis. 

 Harvard College, November, 1893. 



