GEOLOGY OF SARATOGA SPRINGS AND VICINITY 131 



known. It is quite possible therefore that it is here one of the 

 primary minerals of the lava. But the comparatively large amount 

 present, together with the rarity of its occurrence in igneous rocks, 

 enforces caution in attributing such a source to it. In so far as 

 possible derivation from the shale is concerned it must be stated 

 that the associated shales in the vicinity of the knob show no indi- 

 cation of any loss of carbon due to action of the lava, or indeed 

 of any change wdiatever, so that if we look to them as a source 

 we must assume that the process only took place at greater depths. 

 It would be a debatable question whether hydrocarbons, liberated 

 from the shales by the heat of the intrusion, would migrate into 

 the lava; whether they would not rather be driven away from it. 

 Even if taken up why should they have been converted to graphite ? 

 All, or nearly all lavas contain carbon; but on cooling they give it 

 off in combination with oxygen, or \vith hydrogen. Why an excep- 

 tion was made in this case we cannot say. 



Is the lava in place? Stark's knob is a small mass of igneous 

 rock inclosed in shales. The shales are greatly contorted and com- 

 pressed everywhere, and the evidence, both structural and paleon- 

 tologic, shows that they have been overthrust into the district 

 from the east. The question naturally arises, May not the igneous 

 rock have come into the region by overthrusting, along with the 

 inclosing shales? We regret that we are unable definitely to an- 

 swer this question. Were it true, certain of the structural features 

 would receive a simple explanation. The shearing and disloca- 

 tion of the rock would thus be accounted for, as well as its abrupi 

 termination laterally, and the lack of dikes running out from it 

 into the shales. We could understand the reason for the shale 

 wedges inclosed in the lava. More latitude would be given in 

 accounting for the inclusions, abundance of limestone of a single 

 type and absence of all other rocks. The manner of occurrence 

 in the shales, a short and comparatively thick mass of lava im- 

 prisoned in shales along their dip, would also not be so hard to 

 understand. The shales are so cleaved that they usually come 

 apart more readily on the cleavage planes than on the stratifica- 

 tion. It is this character that makes it so difficult to collect fossils 

 from them. It would seem that the explosive action of a vol- 

 canic vent breaking through them would have opened them verti- 

 cally along the cleavage planes instead of following the incline of 

 the dip. 



