370 



K. A. DALY THE OKANAGAN COMPOSITE BATHOLITH 



magma chamber and the hot interior of the earth. Downward enlarge- 

 ment is not only proved in visible cliff sections ; it is demanded as a neces- 

 sary condition of heat supply during spontaneous intrusion. 



The Castle Peak plutonic body thus appears to be a typical stock, an 

 intrusive mass (a) without a true floor, (b) downwardly broadening in 

 cross-section, and (c) intruded in the form of fluid magma, actively, 

 though gradually, replacing the sedimentary rocks with its own substance. 

 It is the most ideally exposed stock of which the writer has any record. 



BATHOLITHIC INTRUSION BY MAGMATIG REPLACEMENT 



Without needing to revert to the accordant discoveries of masters in 

 geology — of Suess, Barrois, Michel Levy, Lacroix, Lawson, Dawson, and 

 many others — we have here, within the Cascade mountains themselves, 



Figure 13. — Plunging intrusive Contact Surface between the Shnilkameen Granite and 

 the Chopaka Roof Pendant. 



Contact shown in broken lines. The vertical distance between the two ends of the 

 contact seen on nearer ridge is 1,600 feet. Drawn from a photograph. Looking east. 



illustrations of magmatic replacement. These authors believe, further, 

 that a stock like Castle peak is but a small batholith; that several asso- 

 ciated stocks jrslj be in truth but protuberant parts of one subcrustal 

 plutonic mass, which with further unroofing would declare itself a typical 

 batholith. These views are consistently upheld by every pertinent struc- 

 tural detail that has yet been made out in the units of the composite bath- 

 olith. Where bedded rocks still remain, they are cross-cut by the granitic 

 bodies. Excellent exposures show that the contact surfaces of the Simil- 

 kameen granite with the Chopaka Mountain and Snowy Mountain schist 

 pendants dip underneath the invaded rocks, proving with every exposure 

 seen the downward enlargement of the batholith (figures 13 and 14). In 



