310 NEW YORK STATE MUSEUM 



much more abundant than hj^persthene. There is great variation 

 in the relative amounts of augite and primary hornblende, and 

 sometimes the latter preponderates.^ 



The two outliers in Franklin county are very small, each only a 

 few square rods in extent. The one is about 6, the other some 8 

 miles distant from the edge of the main mass. Considering their 

 small size, they ;are rather surprisingly coarse, that is, on the 

 hypothesis that they were intruded into the surrounding rocks, 

 yet much of the rock is very gneissold. In the one case the sur- 

 rounding rocks are thought to be later eruptives, the observed 

 contacts seeming to bear out that view, so that the anorthosite is 

 in the nature of a huge inclusion in these eruptives. But there 

 are some difficulties in the way of this interpretation, and, till 

 the material is more thoroughly studied, it can not be positively 

 stated that it is the true one. 



About the other outlier there are no exposed contacts with the 

 surrounding rocks, which are gneisses of uncertain nature and 

 origin, and the relations between the two are wholly uncertain. 



At Rand hill magnificent contacts of the anorthosite gabbro 

 with gneisses thought to belong to the Dannemora formation, are 

 shown and definitely prove the anorthosite to be the younger rock. 



Whiteface type of anorthosite. This name has been proposed 

 by Professor Kemp for a peculiar type of rock, rather uncommon 

 in the Adirondack region, which reaches a considerable develop- 

 ment on, and in the vicinity of, Mt Whiteface. The main mass 

 €f the rock is in Essex county, but it gets over the border into 

 Franklin at Franklin Falls, and into Clinton county on Wilming- 

 ton and Catamount mountains. In both of these situations it 

 becomes much involved with other rocks, and about Franklin 

 Falls it often appears so Interbanded with Grenville rocks as 

 to seem like an integral part of the series. 



The rock has the mineralogy of anorthosite, or rather of 

 anorthosite gabbro, though quite a difi'erent-looking rock from 

 the ordinary types. It is mostly quite thoroughly gneissoid and 

 characterized by the color of the feldspar, which is milky white, 

 even when perfectly fresh and unaltered. In the writer's exper- 



^For a more detailed description of this rock, see 19th An. Rep't N. Y. 

 State Geol. p.r52-r59. 



