350 H. P. GUSHING NORTHUMBERLAND VOLCANIC PLUG 



More recently Kemp, from his study of the mineral waters of the Sara- 

 toga region, some of whose constituents impress him as of probable deep- 

 seated origin, has suggested the possibility that Starks Knob has some 

 significance in the matter and may perhaps be of Tertian 7 age. 6 



A reference to the Newark still seems to the writer the most logical 

 view to take in default of positive evidence to the contrary. If the lava 

 has been overthrust, it may well represent a fragment of a Xewark flow, 

 to some of which it has a strong resemblance, as originally pointed out 

 by Woodworth. That would mean that the date of the overthrusting 

 must be later than the Xewark; but when one contemplates the amount 

 of deformation which the Xewark rocks have everywhere experienced, 

 there is no especial difficulty in that assumption. In any event the 

 amount of deformation which the knob has undergone seems a positive 

 evidence of antiquity. The deformation must have taken place under 

 load, since removed by erosion. The lava is of the effusive type; since 

 being extruded it has been buried, deformed, and then uncovered. To 

 be sure, it lies along the axis of a main valley of erosion, surrounded by 

 relatively weak rocks, so that conditions are favorable to rapid wear ; and 

 glaciation may have been an important factor in the process. But even 

 making every allowance for that, it seems to us that, from this one stand- 

 point alone, the oldest Tertiary is the youngest age that could be ascribed 

 to the lava with any degree of probability. And since Tertiary igneous 

 rocks have been nowhere demonstrated in the country east of the Mis- 

 sissippi, the Xewark age seems to us the more probable. Yet we candidly 

 admit the peculiarity of the rock and its isolated occurrence and have 

 no quarrel with any one disposed to take a different view. It can be 

 legitimately argued that the Saratoga Springs are also peculiar and iso- 

 lated, and that their existence in the same region with the knob is not 

 likely to be ascribable to pure chance. 



To sum up, the knob consists of a small mass of lava of distinctly 

 effusive type. If it is in place, it seems surely a volcanic neck, though 

 it has many characters unlike those of most necks; if not in place, it 

 seems surely a fragment of a surface flow, overthrust into the district 

 from somewhere farther east. If in place, it is younger than the date 

 of the overthrusting, though it may have been somewhat deformed by 

 the final stages of the process: if not in place, it is older. If not in 

 place, we have no definite idea whence it came, nor are any similar frag- 

 ments known. It has some features in common with certain Xewark 

 trap flows and is like some of them in composition. Clear evidence of 

 much shearing of the knob, of such type as to indicate deformation under 

 load, leads to the conviction that the lava can not be an especially recent 

 one. It is noteworthy for its large content of carbon. 



8 Bull. 159, New York State Museum, pp. 61-62. 



