VOLCANIC AND PLUTONIC ROCKS 225 



" The first two species are without question Miocene, The Ficus approaches 

 quite clearly to F. artocarpoides, which is from the Fort Union group (Eocene) of 

 Montana. The specimen is not perfect, and can not therefore be positively deter- 

 mined. If it differs at all from the Fort Union species it must be very little. Yet 

 it may prove to be new. 



"The Cinnamomum is undoubtedly new and a fine characteristic species. It 

 does not approach any described species very closely, yet appears to be of a Ter- 

 tiary type. . . . 



" The two species that can be determined are Miocene and the other two are of 

 Tertiary, probably Miocene, fades." 



VOLCANIC BOCKS 



Two types of volcanic rock occur within the area here discussed. Of 

 these one is andesitic and the other rhyolitic, and both have beds of 

 pyroclastics associated with the lavas. The andesitic rock is of great 

 areal extent to the south and east of the pass. The work of the past 

 season was not sufficient to fully determine the relations of these volcanic 

 rocks, but it seems evident that they are younger than the sedimentary 

 series just considered. Their relation to the great basaltic eruptions of 

 this region will furnish one of the many interesting problems in the study 

 of Cascade geology. 



PLUTONIC BOCKS 



It may seem more logical to discuss this class of rocks before the vol- 

 canic rocks, but in this case the order adopted will be seen to be the 

 natural one. The plutonic rock is for the most part of a granitic char- 

 acter. In the field it has been termed a granite, and the name is here 

 retained. The rock, however, is rather of the intermediate type so im- 

 portant in the Sierra Nevada region, and later petrographic study may 

 show it to be either a quartz monzonite or a quartz diorite. In general 

 appearance it is quite granitic. Quartz is abundant ; both plagioclase 

 and orthoclase are present, the latter being, however, rather less impor- 

 tant than in a typical granite, while hornblende and biotite are of ap- 

 proximately equal importance. In the central portion of the mass this 

 rock, provisionally termed granite, is quite homogeneous in texture and 

 of medium grain. 



More basic phases of the plutonic rock occur, and these are rocks 

 plainly dioritic in composition. An excellent exposure on a glaciated 

 rock wall showed the granitic and dioritic phases to intermingle in the 

 most intricate fashion. The contemporaneous origin of the two was con- 

 clusively shown, and any attempt to separate them would be as futile 

 as it is unnatural. 



The intrusive nature of the granitic mass is shown bv two classes of 



