134 NEW YORK STATE MUSEUM 



If the drill should show that the Bald Mountain limestone was 

 absent below ground at the knob, a quite different face would be 

 put upon the matter. But the drill ^^ris not been at work in the 

 vicinity. 



The age of the lava. Since the suggestion was made that the 

 igneous rock of the knob might ha e some significance in connec- 

 tion with the theory of the juvenile origin of the Saratoga waters, 

 the question of the geologic age v)f the rock becomes of more 

 moment than would otherwise be the case. Unfortunately precise 

 data are quite lacking. 



When Woodworth and Gushing considered this matter, at the 

 time of the original description of the knob, a Newark (Triassic) 

 age was suggested by each of them, independently, as most prob- 

 able. Then, as now, the only positive statement that could be made 

 is that the igneous rock must be younger than the shales which 

 surround it. Even this is not necessarily true, if it has been over- 

 thrust. The shales are of Ordovicic age. There are known in 

 New York three groups of igneous rocks which fulfil that age 

 requirement, the dikes of the Champlain valley, the dikes of cen- 

 tral New York, and the traps of the Newark series. The rock, 

 in its characters, does not at all suggest the Champlain dikes ; still 

 less does it in any way resemble the peridotites of central New 

 York; but it is quite similar to some phases of the Newark traps. 

 Unless we referred it to the Newark we had no alternative but to 

 regard it as representing igneous action of some other date, wilJi 

 no other known representatives in the State. 



That still seems to us the most logical view to take in default 

 of actual evidence to the contrary. The amount of deformation 

 experienced by the knob seems a positive evidence of antiquity. 

 The dislocations already described indicate deformation under 

 load, under a considerable thickness of overlying rock which has 

 since been eroded. The lava is of the effusive type, either a vol- 

 canic neck or a fragment of a lava flow. Since its formation it 

 has been buried under other rock, deformed, and the overlying 

 material removed by erosion. When or under what it was buried 

 we have no means of knowing, since all trace of the material has 

 since been removed ; but if the lava is in place, continental deposits 

 of Newark age seems the most likely supposition. It might have 

 been later continental deposits. To be sure, the knob lies in a 

 main valley of erosion surrounded by relatively weak rocks, so 

 that conditions are favorable to rapid wear. But even making 



