120 NEW YORK STATE MUSEUM 



color (basic) until a rock more like the gabbro than anything else 

 is found. A border phase of the syenite was found a mile east of 

 Lake Clear Junction that exhibits this exceedingly well, the speci- 

 men in mind being taken from a road metal quarry on the north 

 side of the state road. An excellent example can be seen about 

 Long Lake to the south, where the syenite and the anorthosite are 

 in contact and show well-developed border phases. 1 In contrast 

 with the dark phase, the syenite often develops a quartzose type, 

 which with increasing amount of quartz becomes a granitic phase 

 or a true granite, as has already been pointed out. 



A very interesting and instructive igneous contact was brought 

 to light on a reconnoitering trip north of Lake Clear one-fourth 

 of a mile south of Mountain pond. Here, apparently, the syenite 

 in the form of a wide, rusty dike cuts through the anorthosite and 

 has developed curious contact phases. The syenite holds inclusions 

 of the anorthosite as well as fragments of the Grenville rocks. This 

 exposure demonstrates beyond doubt the age relations first estab- 

 lished by Professor Cushing. Associated with the syenite are a 

 number of pegmatites cutting the anorthosites. The more adven- 

 turous summer visitor would be well paid to visit this spot if he is 

 prepared to overcome the difficulties of a district recently ravaged 

 by forest fires. 



In addition to the marked changes in composition, structural 

 differences are to be noted at the contact, as the rocks there often 

 exhibit gneissoid structure and the granulation is more pronounced 

 than is the case in the core of the mass. 



Contacts with the Sedimentary Rocks 

 More striking still are the contact effects often observed at the 

 junction of igneous with sedimentary rocks, especially when the 

 latter are limestones. At such points the changes in structure, 

 texture and composition are often profound. Various vapors that 

 the molten rock contained react with the limestones, giving rise to 

 new mineral combinations that may present a great variety of 

 rocks. A common one is a rock composed almost entirely of red- 

 brown garnets and dark green pyroxenes, very pleasing to the eye 

 and full of interest to the geologist. 2 



1 See the geological map of the Long Lake quadrangle. H. P. Cushing, N. Y. 

 State Mus. Bui. 115, and emphasized by R. A. Daly, " Igneous Rocks and Their 

 Origin," p. 240. 



2 For a fuller discussion of contact metamorphism, see W. Lindgren, " Mineral 

 Deposits," p. 664 ct seq. 



