420 W. J. MILLER ADIRONDACK AXORTHOSITE 



absolutely no evidence for the existence of S3^enite or granite formed as a 

 differentiate between the outer and upper border facies and the lower 

 typical anorthosite. It is therefore evident that the field facts are directly 

 opposed to Bowen's hypothesis of the origin of the anorthosite by the 

 settling of plagioclase crystals. There simply is nothing from Avhich they 

 could have settled, since the chilled border grades perfectly into the true 

 anorthosite, and the border phase is really only more or less gabbroid 

 anorthosite. This must be true, whether we regard the chilled border as 

 simply an outer facies, as advocated by Gushing, or as both an outer and 

 an upper facies of a laccolith, as I have tried to establish above. In other 

 words, in view of the existence of this chilled border without intervening 

 syenite, it is entirely out of the question to interpret the Adirondack 

 igneous complex as even in a general way a "sheetlike mass with syenite 

 above and anorthosite below," as required by Bowen's hypothesis. 



Eelatiox of the Anorthosite to the Grenville Series 

 grextille-axorthosite mixed gxei8ses 



Within the Lake Placid quadrangle I have discovered a number of 

 areas of intimately associated Grenville strata and Whiteface anorthosite. 

 Bowen-^ lays special emphasis on the apparent absence of such areas, and 

 remarks : "In many of the mapped quadrangles it has been necessary to 

 use a color to represent a mixture of Grenville and syenite that defies 

 separate mapping," and that "the anorthosite areas, on the other hand, 

 are very different.'' Since the intimately associated Grenville and anor- 

 thosite rocks have an important bearing on the problem of the anortho- 

 site, I shall describe several of the largest areas somewhat in detail. In 

 many portions of these areas the Grenville has been cut to pieces by dikes 

 and bands of Whiteface anorthosite; in other places the Grenville has 

 been truly injected by the anorthosite, and in many places inclusions of 

 the Grenville occur. In some places the Grenville predominates and in 

 others the anorthosite, but the two rocks are too closely associated to be 

 at all satisfactorily separately represented on the geologic map. It is 

 important to bear in mind that the Whiteface anorthosite, in the areas 

 now to be described, is mostly fully as free from femic minerals as the 

 typical Marcy anorthosite, and in a number of places it is nearly pure 

 plagioclase. 



The largest area within the Lake Placid quadrangle is over 3 miles 

 long and lies between Keene and Upper Jay. For most part the rocks 

 are Grenville hornblende gneiss and pyroxene gneiss which have been cut 



28 N. L. Bowen : Jour. Geol.. vol. 25, 1917, pp. 222-223, 



