GEOLOGY OF SARATOGA SPRINGS AND VICINITY I45 



should be also sliced by big normal faults. So far as we know, 

 this is not the case. If on the other hand the thrust faulting is 

 of a later date than the normal faulting, the overthrust materials 

 should rest on a floor composed of the rocks of the western basin, 

 these latter cut by normal faults which do not rise into the over- 

 lying, overthrust rocks. 



We do not as yet possess decisive evidence on these points. Such 

 as we do have, however, seems to indicate that, in the Saratoga 

 region, the bulk of the thrust faulting is of later date than the 

 normal faulting. 



Cessation of the continental deposits of early Mesozoic age in 

 the eastern troughs was probably brought about by renewed uplift. 

 Then followed a long period of erosion whose final result was a 

 rather thorough wearing down of the region to a comparatively 

 level plain. Such an erosion plain is called a peneplain ; a peneplain 

 of this date was produced quite generally throughout the Appala- 

 chian region and eastern Canada, and it is reasonable to assume 

 that it was also produced here. 



CENOZOIC HISTORY 



At the close of the Mesozoic the region was again uplifted. The 

 low altitude peneplain which had been produced over the Adiron- 

 dack region was elevated some 1500 feet or more, and rapid 

 erosion of its surface began. Stream valleys were cut down and 

 broadened. It is the depth of the valley cutting below the old 

 peneplain level which enables us to estimate the amount of the 

 uplift. The divides between the valleys, however, have been but 

 little worn down during the time that has passed since the uplift. 

 These divides rise now to uniform levels, the levels of the old 

 peneplain. An observer, standing upon one of these divide sum- 

 mits and looking abroad to the others, receives the impression of 

 standing upon the surface of a plain and has merely to imagine 

 the valleys refilled with material in order to picture the plain as 

 it was at the time of the uplift. 



This old peneplained surface is readily made out over most of 

 the Adirondack region. But in the extreme east it seems to fail 

 and the divide summits rise to very discordant levels instead of 

 being uniform. This we take to mean that here renewed slipping 

 along the old faults occurred as a phase of the uplift ; that the 

 Champlain trough displayed anew its tendency to sag relative to 



