REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r43 



At 4J miles from the junction is a rock cut in the first anortho- 

 site seen (903). II is of the anorthosite gabbro tyipe and inter- 

 ■esting in showing all gradations from quite coarse to very finely 

 mashed rock. In fact, the granulated portions are much finer 

 grained than usual, have a greenish tinge, and in com'bination 

 with the dark blue black labradorite augen produce a very strik- 

 ing looking rock. 



A small cut ^ mile farther furnishes similar and very interest- 

 ing material (905). The rock is pretty thoroughly granulated, 

 though numerous small labradorite augen remain. The granular 

 portion has a strong reeemhlance to the usual augite syenite. 

 The rock j& an anorthosite gabbro, with 10^ to 15^ of minerals 

 other than feldspar, these being the usual magnetite, garnet, 

 augite, hornblende, apatite, zircon and pyrite. A little quartz is 

 present as a by-product of the feldspar-magnetite interaction 

 which resulted in the garnet formation. Of the feldspar in the 

 elide (none of the large augen appearing) slightly less than one 

 half show^s albite twinning, the maximum extinction found in the 

 several sections properly cut being 12°, indicating andesin. Of 

 the untwinned feldspar the larger portion shows intergrowths, 

 partly microperthite and partly of the micrographic type. The 

 intergrowths seem distinctly primary, though some of the andeein 

 show^s a tendency toward such intergrowths as well. Optical 

 teste of cleavage pieces of the large augen show these to be 

 labradorite. 



A portion of the rock w^as crushed, and specific gravity deter- 

 minations of these feldspars w^ere made. At 2.659 the first con- 

 siderable quantity of feldspar fell, and this is closely the gravity 

 of acid andesin. The last and greater part of the remainder 

 fell at 2.569, though, as the liquid was slowly diluted down to 

 this strength, a little feldspar fell from time to time, indicating 

 the presence of a slight amount of intermediate composition. A 

 chemical analysis and further discussion of this rock, as well as 

 of that from the 3i mile cut (906), will be found on a later page. 



At 5 miles from the junction and shortly before reaching 

 Rollins pond is another cut in anorthosite gabbro, specially rich 



