GEOLOGY OF SARATOGA SPRINGS AND VICINITY I33 



we can not relieve ourselves of the suspicion that it may, after all, 

 be an overthrust mass, a fragment of a surface flow which came 

 up through and was poured out upon a surface of limestone, thus 

 acquiring its inclusions, and later on thrust westward coming to 

 rest with rocks with which it had originally little to do. 



The inclusions. The difficulty of accounting for the limestone 

 inclusions in the lava has already been mentioned. The inclusions 

 are many, and all of one kind of rock, which seems perhaps re- 

 ferable to the Bald Mountain limestone, but certainly to no other 

 of the rock formations of the region. The knob lies in the midst 

 of overthrust shales. Just what their thickness is at the spot we 

 have no means of knowing; but it is quite likely considerable, since 

 they extend 5 miles farther west before thinning out to disappear- 

 ance. In considering the manner of overthrusting in such weak 

 shales it seems reasonable, if not obligatory, to suppose that the 

 thrust was carried by some strong, competent stratum, on top of 

 which the shales were carried westward. The Bald Mountain 

 limestone is the first formation of the sort beneath the Normans- 

 kill shale, in the eastern basin section, and it is therefore not un- 

 reasonable to suppose that it is present underneath the shales at 

 Stark's knob. If so it probably rests on the western basin rocks, 

 most likely on Canajoharie shale. That the structure as a whole 

 is not so simple as this, that the shales are jumbled indiscrim- 

 inately together to a certain extent, is shown by the presence of 

 Schaghticoke (Dictyonema) shale in the midst of the Normans- 

 kill near the knob. Were fossils more abundant, many such mix- 

 tures might be found. This suggests that a confused mixture 

 of shales may have moved west even beyond the competent stratum 

 which carried them, falling and being pushed in front of the main 

 mass. The Bald Mountain limestone therefore may, or may not, 

 be present below ground at the knob. If it is present it lies nearer 

 the surface than any other limestone, with shales both above and 

 below ; and it is likely also to be in somewhat shattered condition, 

 so that it would readily furnish inclusions to an igneous rock ris- 

 ing through it. The limestone inclusions can therefore be plausibly 

 accounted for on the theory that the lava is in place. The lack of 

 inclusions of shale is not thus explained ; but the carbon content 

 of the lava may have come from the shale, and its failure to fur- 

 nish inclusions may be due to the physical nature of the rock. 



So far as the inclusions are concerned, therefore, they do 

 not aid in the decision as to whether the lava is in place or is not. 



