494 PROCEEDINGS OF THE liATJONAL MUSEUM. vol.57. 



along the contact with the finer-grained phase which is free from 

 epidote. This is one of the types of agglomeratic intrusion referred 

 to elsewhere. (See pi. 39 A.) 



S'pessartite, Rex Mine N'menule. — A specimen collected by Doctor 

 Umpleby and examined only in thin section, shows a holocrystalline 

 fine-grained nonporphyritic lamprophyre, consisting in large part 

 of prismatic hornblende, witli less abundant plagioclase. The horn- 

 blende is not so well crystallized as is usual in these rocks. The 

 plagioclase is zoned, but twinning is rare. The rock contains fre- 

 quent patches of serpentine suggestive of original olivine, in each 

 case surrounded by a rim of hornblende. The rock is very similar 

 to that of the Standard dike. 



Olivine-augite voffesite, Frisco Mine. — This rock, which cuts 

 sharply across the ore body on the l,COO-foot level of the Frisco 

 mine west of the shaft, is seen under the microscope to be composed 

 of large phenocrysts of augite, rather sparsely scattered through a 

 fine grained holocrystalline groundmass consisting of the usual 

 green-brown hornblende and feldspar. The augites are perfectly 

 fresh and show well-developed cleavage. Occasionally there is a 

 suggestion of very pale green color and barely perceptible pleochro- 

 ism indicating some admixture of the aegirite molecule. The feld- 

 spar is in such minute and poorly characterized altered individuals 

 that its character must remain in doubt. While the appearance re- 

 sembles twinning it is probable that it is orthoclase of the fibrous 

 character noted elsewhere — an assumption supported by the alkalic 

 appearance of the augites. Sparsely disseminated large phenocrysts 

 now consisting entirely of talc dotted with iron ore are surrounded 

 by hornblende and represent original olivine. (See pi. 37B.) 



Vogesite, lower part of R. R., E. Fork of Ninemile Creek. — This 

 rock, which was collected by Calkins, is a good example of the ag- 

 glomerate or mixed dike so common among these rocks. In the hand 

 specimen it is quite plainly made up of two kinds of rock, one a 

 rather coarse granular aggregate of hornblende and feldspar form- 

 ing inclusions in a matrix of darker colored material composed of 

 hornblende prisms in an indeterminate grayish base. The thin sec- 

 tion which evidently was cut from the latter portion of the specimen 

 shows phenocrysts of hornblende of the usual type in a very fine 

 grained ground apparently consisting of minute grains of orthoclase. 

 Large patches of chlorite surrounded by rims of hornblende suggest 

 original augite. Quartz in interstitial grains is common. Iron ore 

 in scattered grains is the only other prominent accessory. 



Other lamprophyric dikes. — The lamprophyric dikes are present 

 over the wliole of the Coenr d'Alene district and surrounding ter- 

 ritory. There is scarcely anywhere an artificial exposure of Prichard 

 formation rocks which does not contain one or moro of tlie dikes imrx< 



