GEOLOGY OF THE PORT LEYDEN QUADRANGLE 1 7 



vicinity of the contact and which while less abundant, are found 

 throughout practically the whole extent of the bathylith." Judg- 

 ing from his descriptions of the amphibolites, the inclusions in 

 the Port Leyden region are very similar to them and, although 

 we have here no such positive evidence for their origin, the ex- 

 planation above given by Professor Adams becomes very sug- 

 gestive at least. 



In a general way at least, another distinction from the syenite 

 is the more complete granulation of the granitic gneisses. Under 

 the microscope the cataclastic structure is always well exhibited, 

 sometimes to a remarkable degree. The quartzes were most 

 badly broken by the grinding action and strain shadows are 

 common. 



In thin section the typical red granitic syenite from near the 

 lower road crossing on Otter creek is seen to consist of about 

 60^ of feldspar; 35^ of quartz; 3^ of hornblende; 2;^ of mag- 

 netite, and a very little zircon and apatite. The feldspar is 

 chiefly microperthite accompanied by some anorthoclase and a 

 little oligoclase. Red hematite stains are common in the sec- 

 tions. Closety associated with this typical rock, but always in 

 subordinate amount, is a gray, less quartzose and more truly 

 syenitic rock. In all of the sections of the granitic syenite exam- 

 ined the feldspar ranges from 60 to 70^. Microperthite is the 

 chief feldspar, while anorthoclase ranges from absence to 20;^, 

 and oligoclase never exceeds 5^. The quartz range is from 25 

 to 4ofc. Hornblende is always present but never above 5^. Bio- 

 tite is often absent and never exceeds 2^. From i to 4^ of 

 magnetite alwa3^s occurs. Small crystals of apatite and zircon 

 are common. 



It seems certain that this red granitic gneiss is a differentia- 

 tion phase of the normal syenite gneiss. Except for the greater 

 granulation and somewhat higher quartz content, microscopic 

 study shows no difference between the rocks. In the field no 

 sharp line of separation can be drawn. The normal syenite in 

 general seems to become more quartzose toward the north so 

 that in this respect, at least, the syenite around Partridgeville 

 closely approaches the granitic syenite. The writer is inclined 

 to the belief that the passage from one rock to the other is much 

 like that described by Smyth in the Diana area some 20 or 25 

 miles northward. He says : ^ " Passing southward from the 

 latter (limestone formation) the syenite at first slowly and irreg- 



^ loc. cit. p. 481-82. 



