January 26, 1900.] 



SCIENCE. 



131 



of Salmon river, about three-fourths of a 

 mile distant from Mt. Courtney, there is 

 another granite batholite but it is composed 

 of an entirely different type of granite. It 

 contains the ordinary quartz, feldspar and 

 biotite, but in addition, it abounds in well- 

 formed crystals of dark green and black horn- 

 blende. The feldspar being largely plagio- 

 clase, it is a quartz-mica diorite, although its 

 general appearance in the field is distinc- 

 tively that of a granite. In fact, it is the 

 rock commonly designated, by students of 

 the Sierra Nevada region, granodiorite. It 

 is finer grained and a darker gray in color 

 than the Courtney granite. 



This massif of granodiorite is at least a 

 mile in length and one-half mile in width. 

 It is one of a series of such granite masses 

 scattered through the Sierra Costa moun- 

 tains eastward from Mt. Courtney, some of 

 which are as much as three miles in width. 

 They all contain the large constituent of 

 hornblende, and are characterized by spots 

 of darker color, like included boulders of 

 diorite-porphyrite, but which are probably 

 concretionary in origin. 



It is difi&cult to comprehend how such 

 great masses of granite could be injected 

 into the stratigraphic series, displacing the 

 strata for miles. Mt. Courtney is but one 

 of a series of high granite peaks extending 

 southwest from it and apparently consisting 

 of the same great massif of coarse-grained 

 biotite granite, which may be ten miles or 

 more in width. The strata of serpentine 

 and schist must have been forced apart and 

 up into high mountain masses, of which 

 ■even Mt. Thompson, altitude 9345 feet, is 

 but an insigaificant remnant. 



Between Mt. Courtney and the massif of 

 granodiorite about three-fourths of a mile 

 east of it, there is a block of mica and horn- 

 blende schists wedged in between the two 

 granite masses. This dips steeply east- 

 ward, away from the Courtney granite and 

 toward the granodiorite. As it approaches 



the latter it becomes nearly vertical, but 

 the strata are cut off by the granodiorite. 

 The contact is finely exposed and shows no 

 contact metamorphism. The dark green 

 hornblende schists are absolutely un- 

 changed to the very contact. Fragments 

 of all sizes up to 100 cubic feet, of the 

 hornblende schist are included in the 

 granodiorite from the contact in places, 100 

 or more feet distant. Some portions of it 

 are a veritable breccia of schist cemented 

 by granodiorite. 



Now, the edges of all fragments are 

 sharp and the corners angular. Nowhere 

 is there the least evidence of partial fusion 

 of the schist material even along the edges, 

 by the heat of the great mass of ' melted ' 

 granodiorite in which it had become in- 

 cluded. If the latter was very hot, it ap- 

 pears evident that during the long time 

 which such a great mass must have re- 

 quired in cooling, the hornblende and 

 quartz, of the schist fragments must have 

 partially fused. The failure of this to occur 

 to even the slightest degree, implies, in my 

 mind, that the granodiorite was not very 

 highly heated — not nearly so much so as 

 other dike rocks of the same region. Yet 

 that it was in a highly liquid condition is 

 proved by its injection into the finest cracks 

 of the adjoining schist. In short, I believe 

 there is here abundant evidence to demon- 

 strate a perfect fusion without great heat, 

 a sort of ' wet fusion,' we may suppose, 

 due to the presence of heated alkaline 

 waters. The fragments of hornblende schist 

 were impervious to this water, the heat not 

 sufficient to produce a ' dry fusion,' and 

 hence the present phenomena, described 

 above. As this locality may prove a very 

 interesting one to students of igneous 

 geology, I will give it as the vicinity of 

 Lake Catrina, on the mountain ridge just 

 east of the head of the south fork of 

 Salmon river. 



The age of all the granites of the Sierra 



