108 NEW YORK STATE MUSEUM 



There is no question that a more detailed investigation of these* 

 rocks will necessitate their subdivision into a number of minor 

 types, some of which may be sharply marked off from one another 

 and represent wholly separate intrusions. Pending such investi- 

 gation, it is unwise to attempt subdivision. It may be said that 

 these rocks vary exceedingly from place to place, both in com- 

 position and in structure, often with great rapidity, recalling the 

 gabbros in this respect. In part they are granites, in much 

 larger part augite or hornblende syenites, both with and without 

 quartz. So far as they have been carefully studied, all the 

 syenites of Franklin county belong to the type of these rocks com- 

 prised under Brogger^s name akerite. 



The main areas of syenite in the county are indicated on the 

 accompanying map, and may be called the Loon lake, Tupper 

 lake, St Regis river and Salmon river areas. The Loon lake area 

 may prove to fall into two distinct areas on farther study, the- 

 second of which may be called the Saranac river area, excellent 

 exposures appearing along the river from Franklin Falls up> 

 nearly to Saranac. 



Extending northward from Franklin Falls and thence along- 

 Alder brook as far as the north branch of the Saranac, is a chain: 

 of low hills of a peculiar, coarse, brown gneiss, which is regarded 

 as belonging to the augite syenites, though so weathered that it 

 is almost impossible to get fresh material. In the one or two 

 places from which such has been obtained, as from the roadside 

 near Alderbrook postomce, it is not quite certain that it is of the 

 same rock; but, if so, it is augite syenite. These brown rocks 

 vary from place to place quite as the ordinary syenite does, and 

 differ mainly in the less pronounced spindle form of the quartz 

 when present. The hills formed of this rock are low but very 

 steep sided, producing an unmistakable topography from which 

 the character of the rock may be predicted with certainty (see 

 pi. 6). The rock has cataclastic structure, is certainly igneous. 

 and is a syenite, in large part a quartz-augite-syenite, though of tens 

 with much hornblende. 



