Spurr — Scapolite Rocks from Alaska. 313 



gate of plagioclase, scapolite, and green hornblende, with 

 accessory pyroxene, quartz, epidote, and pyrite, and this rock 

 is termed a plagioclase-scapolite diorite. It is stated in the 

 pamphlet referred to that "although the derivation of at least 

 a part of the hornblende of these rocks from pyroxene is well- 

 nigh certain, the derivation of the scapolite from plagioclase, 

 which, as already stated, has been pretty clearly proved in the 

 case of the Norwegian rocks, is not so evident in these similar 

 rocks from Canada." Also, Dr. A. P. Coleman reports from 

 Ontario a scapolite rock consisting of hornblende, plagioclase, 

 and scapolite, in which the scapolite was evidently primary.* 



Finally, scapolite rock occurs in the white limestone of JSTew 

 Jersey at many localities and in large amounts, the rock con- 

 sisting in one locality of scapolite, hornblende, pyroxene, and 

 sphene, and in another locality of the same minerals with the 

 addition of a little plagioclase. These dikes are evidently 

 igneous, and fumarolic or gaseous action has been suggested as 

 taking part in their formation. f 



In addition to these granular scapolite rocks, scapolite 

 gneisses and amphibolites have been described from various 

 places.;}: 



Origin and Classification of the Alaskan Scapolite Hocks. 



In the locality on the Yentna River which has been described 

 the main intrusive rock of the country was noted in the field 

 to be a biotite granite, but of this, unfortunately, no specimen 

 was retained. Dikes of qnartz-feldspar rock or alaskite,§ 

 which were found cutting the granite, have been carefully 

 examined microscopically, and connected with this alaskite 

 were rocks transitional into the granite, and quartz veins some- 

 times containing tourmaline. The specimen of scapolite rock 

 was from a large mass forming bluffs 40 feet high, and seemed 

 typical ; it is certain that this rock occurs in notable quantity, 

 but in just what proportion to the other dikes is not certain. 

 All these dikes cut an ancient igneous rock, which was shown 

 in one case to be a hornblende syenite and again a hornblende 

 diorite. 



In the second case which has been described, namely, the 

 quartz-scapolite rock from the Knskokwim River, the scapolite 

 dikes were associated with a number of other siliceous dikes. 

 Those which were examined microscopically, besides the scapo- 

 lite porphyry, are an alaskite porphyry and a granite porphyry. 



* See Zirkel's Lehrbuch der Petrographie, vol. ii, p. 783. 



fF. L. Nason, Annual Report of the Geological Survey of New Jersey, 1890, 

 p. 33. 



JZirkel, op. cit., vol. iii, p. 339. 



§ See author's paper on Classification of Igneous Rocks according to Composi- 

 tion ; Am. Geol., xxv, April, 1900, p. 210. 



