REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r93 



Quartz Orthoclase Albite Anorthite Hornblende Magnetite 

 12.67^ 33.42 36.84 4.17 12.02 1 



Total 100.12 

 This can not depart widety from its actual compo'Sition. The 

 rock is an acid quartz syenite, in its high soda percentage show- 

 ing affiliation with the monzonite group. 



Diabase dikes 



Nearly a mile east of the depot the rock cliff is broken by a 

 small gully, apparently along a fault line. Forming the east w^all 

 of this gully is the largest diabase dike which it has been the 

 writer's fortune to see in northern New York. It is at least 120 

 feet wide, bears n. 70° e., and shows numerous and large porphy- 

 ritic feldspars, often an inch and more in length. As wonld be 

 expected from its width^ the dike rock is fairly coarse grained, 

 though with the usual chilled borders. 



The rock is not fresh. So far as can be told, it consisted simply 

 of plagioclase, augite and magnetite. There is no indicationi of 

 oliyin. As is the case with most of the Adirondack diabases 

 which lack olivin, the feldspar preponderatesi miuch over the 

 augite, and the structure is not ophitic, though the feldspars are 

 lath-shaped. Prof. Smyth informs me that there are specimens 

 from two diabase dikes from Little Falls in the Hamilton col- 

 lege collections. The interest attaching to their presence is that 

 such dikes are very rare in the southern and western Adirondiacks, 

 though abundant on the north and east. The fact that at least 

 two are present in this small ontlier is an indication that they 

 probably reappear in force here under the Paleozoic cover. It is 

 inferred that these dikes are pre-Cambrian, since that is the age 

 of the Adirondack diabase^ and since the dikes which are found 

 cutting the Paleozoic rocks of the vicinity are of a wholly differ- 

 ent rock, alnoite. 



Age of the syenite 



Since this outlier shows no other crystalline rocks than the 

 syenite and diabase, any discussion of its age can be but tentative. 

 Yet, since the various pre-Cambrian outliers expose no rocks 



