THE GEOLCGY OF THE SYRACUSE QUADRANGLE 5 1 



In comparing the dike rocks, Smyth says that the Butternut 

 street rock bears a strong family resemblance to that at Green street 

 and at Dewitt, with perhaps less mica, and rather more perofskite, 

 while only one section showed the tiny crystals of pyroxene that 

 are so abundant in the Dewitt dike. 



In speaking of the dikes of the county he says : ''Apparently, 

 then, the petrographic affinities of this group of dikes is with the 

 melilite rocks rather than with the peridotites, and this is very in- 

 teresting in bringing them into close relationship with the Manheim 

 dikes, and in determining another occurrence of a rare variety of 

 rock (alnoite)." 



As might be expected, the larger Syracuse dikes contain many 

 inclusions or fragments of the underlying rocks that were torn off 

 from the sides of the fissure during the ascent of the molten rock. 

 There are fragments of the inclosing and immediately underlying 

 sedimentary shales, limestones and sandstones as well as of the 

 deeper underlying Precambric crystallines. Most numerous are 

 the fragments of the inclosing Gamillus shales. Mr P. F. Schneider 

 has in his possession a piece of limestone containing Trenton fossils 

 that was taken from the dike rock. One fragment of gneiss was 

 taken from the Green street dike that measured 8 by 14 inches, 

 one of the largest inclusions. 



Neither the inclusions or the wall rock show much metamorphism. 

 The limestone and the shale fragments have a very thin crust, a 

 mere fraction of an inch, that is baked by the heat of the dike. 



The age of the dikes remains unknown. The Syracuse and De- 

 witt dikes penetrate the Camillus shales, the Ithaca and 'Ludlowville 

 ones penetrate the Upper Devonic. It is probable that they are of 

 the same age. There have been two great disturbances of the 

 Paleozoic rocks of the eastern states : one at the close of the 

 Ordovicic, the Taconic revolution, and one at the close of the Car- 

 bonic, the Appalachian revolution. If the Syracuse intrusions are 

 of the same age as the others, the intrusion could not have been 

 during the Taconic disturbance. While it is possible that the intru- 

 sions might have taken place during the Appalachian disturbance, 

 there is no evidence to prove that they might not have occurred at 

 a still more recent date, as during the Mesozoic period when the 

 great trap intrusions took place along the Appalachian area. The 

 absence of any glacial materials in the dike rock would indicate that 

 the intrusion took place before the glacial period. 



