266 Plrsson and Washington — Geology of Red HUl, JV. PL. 



Petrography. 



It is a well-known fact that in those places which have been 

 centers of intrusion of alkalic magmas there are commonly a 

 considerable variety of igneous rocks represented and this 

 applies more especially to those which are of high sodic 

 content. It was thought that this might prove to be the case 

 when the study of Red Hill was begun, as up to this time its 

 investigation had not been undertaken by any petrographer ; the 

 work of Bayley having been carried out on material sent him 

 by a local resident, and there being no evidence in his writings 

 that the locality was visited by Hawes, who did some field 

 work and collecting in other parts of the White Mountain 

 region. 



The study of the region lias shown, however, that there is 

 not a marked complex with many types represented. The 

 main massif consists of miaskose which grades in one direc- 

 tion into • umptekose and in another into nordmarkose, or in 

 the terminology generally used at present it is composed of 

 a foyaite type of nephelite syenite which passes into umptekite 

 and nordmarkifce varieties of alkalic syenite. These types are 

 described in the present paper, while another, that will shortly 

 appear, will be devoted to the dikes of the region, which 

 include porphyritic miaskose (nephelite-syenite porphyry), 

 liparose (paisanite), nordmarkose (bostonite), camptonose 

 (camptonite), etc., and to a general discussion of its petrology. 



Hornhlendic-grano -miaskose {Foyaite). 



The occurrences and extent of the main type of syenite lias 

 already been described and for purposes of petrographic stud} 7 

 and analysis the material exposed in the quarry or pit in the 

 field across the road from the Home farmhouse has been selected. 

 As stated, it is the type which apparently composes the greater 

 volume of the massif. 



Megascopic. — Holocrystalline; medium-grained from 2-5 nim , 

 average 2-3 ; pale gray, rather sparsely dotted with black horn- 

 blendes very short, thick, columnar, whose cross sections aver- 

 age 5 by 3 mm and sometimes grouped ; nephelite, smoke-gray 

 to greenish atid oily, abundant and retreats and darkens on 

 weathering, giving pitted surfaces. Yery rarely an occasional 

 flake of biotite is seen in some specimens; no other minerals 

 of megascopic importance. 



Microscopic. — The following minerals were observed in thin 

 sections: iron ore, apatite, zircon, titanite, wohlerite, biotite, 

 segirite, segirite-augite, diopside. cataphorite-arfvedsonite, vari- 

 ous alkalic feldspars ; nephelite, sodalite, cancrinite and several 

 alteration products. 



The iron ore is irregularly distributed ; in sections from the 

 type in the quarry it is nearly wanting, occurring only in occa- 



