ADIRONDACK MAGNETIC IRON ORES 93 



45 , with rarely one to the west of north. The dip is uniformly 

 toward the west. In many places the foliation is too obscure to 

 permit determinations with any certainty. 



Augite syenite. This rock occupies two distinct areas at least 

 within the district. The one near Ausable Forks already mentioned 

 is the larger and more typical of the normal character of the syenite. 

 As near as the limits can be drawn it forms practically a connected 

 mass or boss, the surface of which is coextensive with that of the 

 dome-shaped hills lying between Ausable Forks and Palmer hill. 

 The exposure south of the Ausable is probably an offshoot from 

 this mass. Compared with the gneiss of the region the syenite shows 

 marked differences even in hand specimens. Its color on fresh 

 surfaces is green, with a suggestion of gray or yellow at times, 

 while the fracture is that of a close grained igneous rock, con- 

 ditioned by its massive texture. Feldspar and magnetite are the 

 minerals most apparent to the unaided eye. Under the microscope 

 the former is seen to be almost entirely microperthite, while asso-' 

 ciated with it are augite, hypersthene, hornblende, quartz, zircon, 

 apatite and rarely a light colored garnet. The feldspar is built up 

 in stout anhedra between the interstices of which the quartz occurs 

 in irregular grains. On the borders, especially on the east side of 

 the mass, the rock is apt to be more quart zose and the grains attain 

 such dimensions that they are readily distinguishable. 



The second occurrence of the syenite is on Arnold hill, a few 

 hundred feet west of the Nelson Bush mine. It is here quite differ- 

 ent in appearance from the first, having a mottled aspect which is 

 induced by the abundant hornblende mixed with the feldspar. 

 Plagioclase constitutes a large proportion of the feldspar. The 

 rock is to be regarded as a basic phase of the syenite, near the 

 borders of the gabbro rock group. 



Gabbro. The only intrusion of gabbro in the gneiss series of the 

 district that has been found is on the south bank of the Ausable, a 

 mile east of Ausable Forks along the Clintonville road. It is a 

 coarse dark rock somewhat laminated but with the peculiar mot- 

 tling that is so often associated with gabbroic rocks. The constitu- 

 ents are mostly hypersthene, hornblende and labradorite. The 

 occurrence is doubtless to be ascribed to an outlying intrusion from 

 the large anorthosite-gabbro area to the south. 



Dikes. Diabase dikes are conspicuous features of the geology of 

 the ore bodies. They intersect the latter in different directions, 

 apparently without following the joint systems of the walls. Their 

 thickness ranges up to 15 feet, the maximum reached by two dikes 



