Il6 NEW YORK STATE MUSEUM 



ihc ( irciuille belt, is undoubtedly similar in origin and age. It is 

 not certain, of course, that the total deformation along- these lines 

 is of Mesozoic Age, but in some cases there is no doubt that a large 

 amount of the displacement is Mesozoic. Many other fault lines 

 have such uncritical relations that it is impossible to place them in a 

 time scale, but it may well be that a good deal of the faulting trace- 

 able in the physiographic expression of this district belongs to this 

 period instead of to earlier ones. At least it is certainly a mistake to 

 credit even the bulk of the faulting to earlier periods. • A more 

 critical evaluation of the evidence doubtless will support the proposi- 

 tion that all the deformation periods developed faults and in some 

 cases probably the same fault lines were the seat of new movement ; 

 but how much belongs to the different individual deformation epochs 

 is not determinable. 



The Mesozoic deformation, however, seems to have been of the 

 nature of block faulting and is represented by little and wholly inci- 

 dental crulmpling or folding. Such an effect on a small scale Tnight 

 be due simply to slight crowding of the blocks. Faulting of the 

 Appalachian time was dominantly of thrust type. That of the 

 Taconic epoch is less definitely known and largely hypothetical, and 

 those of earlier time are quite obscured by subsequent modification. 

 The greatest prominence, therefore, might be expected to attach to 

 the last two epochs and these might well be separated on the basis 

 of character of deformation, that is whether, on the one hand, essen- 

 tially a thrust with its accompanying adjustments or, on the other, 

 essentially block faulting with little other distortion. This separa- 

 tion might be made more perfectly in some other kind of region than 

 in one of granites and gneiss. In such forjnations as these, some 

 of the evidences to be expected are either obscure or entirely lacking. 



Most of the faulting belonging to the Mesozoic seems to have been 

 of Triassic age. This is judged to be true chiefly because there is 

 an obscure development of a peneplain on the gneisses of the High- 

 lands. If much of the deformation were Post- Cretaceous, 

 the peneplain ought to be interrupted and abruptly deformed. This 

 does not seem to be prominent enough to warrant emphasis, 

 l)ut it may very well be that this is exactly the explanation 

 for a curious discordance of peneplain level at the southerly margin 

 of the Highlands. It seems as well established as any feature of 

 this kind its anywhere that the top of the Palisade ridge from New 

 York City to the vicinity of the Highlands on the west side of the 

 Hudson coincides approximately with the Cretaceous peneplain. 

 This rises very gradually from near sea level at New York City to 



