146 NEW YORK STATE MUSEUM 



the gorge of the Mohawk at that place and extends eastward for 

 nearly 2 miles; the syenite forms the first lines of cliffs on either 

 side, rising to a maximum of about 200 feet above the river, above 

 which is a second steep scarp consisting of the exposed edges of 

 Ordovician limestones whose base rests unconformably upon the 

 crystallines. 



The Little Falls syenite has a dark green to nearly black color, 

 changing to yellowish or brownish on weathered surfaces. The 

 texture is mostly fine granular, the result of mashing after intrusion. 

 There are occasional feldspar " augen " in the midst of the com- 

 minuted minerals which may be taken as evidence that it once 

 possessed a much coarser grain. Over much of the area it has 

 a mashed gneissoid appearance and is thinly jointed, the joints caus- 

 ing a platy structure in places like that of a schist. There has been 

 some infiltration of iron oxides along the joints and locally these 

 extend into the body of the rock, filling the minute cracks and 

 pore spaces and changing the color to a brick red. 



In composition, the rock varies considerably from place to place 

 and in many samples of the outcropping portion shows a wide 

 departure from the syenitic type. In the eastern section, the mass 

 develops very dark basic phases which are close to gabbro in min- 

 eral composition and in the hand specimen much resemble a fine- 

 grained gabbro. Such phases occur along the tracks of the Dolge- 

 ville railroad, near the quarries of the Syenite Trap Rock Co. The 

 feldspar constituents, however, belong to the alkali varieties, with 

 subordinate amounts of lime-soda feldspar of andesine or oligoclase 

 type, so that the material can not be classed as gabbro. Quartz is 

 also present, as it is elsewhere in considerable abundance. The 

 dark minerals include hornblende, hypersthene, biotite and garnet. 

 Among minor ingredients are apatite, quartz, titanite, magnetite and 

 pyrite. In the more acid phases, there is about 75 per cent of 

 feldspar, chiefly microperthite, about 10 per cent of quartz and be- 

 tween 10 and 15 per cent of the iron-magnesia minerals. The basic 

 examples carry as much as 50 per cent of the latter ingredients. 



Throughout the exposure occur scattered patches and bodies of 

 a reddish granitic rock, some of which seem to be in the nature of 

 inclusions, rather than dikes. Such are found in the north face of 

 the Trap Rock Company's quarry. Cushing regards the red granite 

 found in the western section around Little Falls as intrusive in 

 the syenite. 



