REPORT OF TEE CHIEF ASTRONOMER 473 



SESSIONAL PAPER No. 25a 



the following silica percentages, arranged in order, from oldest to youngest: — 

 63-30 and (68-43 -x); 66-55; 67 to TO; 71-21; 76 dr. 



On the other hand, if we include the Kruger alkaline body, we have two 

 tandem series, one begun by the Chopaka and other old basic intrusives and the 

 later series begun by the basic-alkaline Kruger intrusive. These two series were 

 separated by millions of years, representing an interval in which the Osoyoos 

 and Remmel batholiths were completely crystallized, crushed, eroded, and then 

 deeply buried beneath the Pasayten geosynclinal — all before the Kruger body 

 was intruded.* It thus seems highly probable that the Kemmel-Osoyoos grano- 

 diorite and Kruger alkaline body were not in direct genetic connection. Each 

 of the two series of intrusives was inaugurated by a definite revival of plutonic 

 energy and, in each case, the first magma to be injected was a basic magma. In 

 each case the subterranean heat sufficed to prepare huge, subjacent masses of 

 granodiorite. The granodiorite closed the first series so far as true batholithie 

 intrusion in this region was concerned. In the second series the conditions 

 favoured the still later generation of the alkaline Cathedral granite in its two 

 phases. 



Corresponding to the succession of chemical types, the members of the 

 composite batholith illustrate a law of decreasing density with decreasing age. 

 This relation is shown in the following table (XXXI. ), in which the average 

 specific gravities of the respective fresh, holocrystalline rocks are noted. As 

 usual the readings were made at room temperatures. Where possible many large 

 hand-specimens were employed in each determination. Again it is observed 

 that the average specific gravities fall into two regular series, the second being 

 initiated with the value for the Kruger alkaline body. Including only the 

 undoubtedly batholithie members, the sequence from the Osoyoos-Remmel to the 

 younger phase of the Cathedral granite is quite regular. From the known 

 behaviour of holocrystalline rocks as they are melted, it is practically certain 

 that the densities of the successively intruded magmas followed the same law 

 of gradual decrease. 



* During this long interval the Lower Cretaceous Pasayten agglomerate of augite 

 andesite was erupted from local volcanoes on to the eroded surface of the Eemmel 

 batholith. This formation will be described in the next chapter; its occurrence is of 

 interest in the present connection as showing that the two batholithie, granitic series 

 were separated in time by a period in which magma much poorer in silica afforded the 

 staple eruptive of the region. To the probably Tertiary Similkameen batholith the 

 Pasayten andesite eruptive bears a chronological relation which is analogous to that 

 of the late Paleozoic andesites (greenstones) of the Okanagan range and of the Anar- 

 chist plateau to the Eemmel-Osoyoos batholith. The eruption of the Pasayten agglo- 

 merate as well as of the Kruger alkaline body clearly shows the justice of regarding 

 the magmatic history of the Okanagan composite as divisible into two series, each 

 begun by eruptions of basic or relatively basic rock. 



