REPORT OF THE CHIEF ASTRONOMER 497 



SESSIONAL PAPER No. 25a 



surface through vertical depths of from 300 to 2,200 feet. In every case the 

 contact surface dips away from the granodiorite, plunging under sandstone or 

 argillite and truncating the beds. The angle of this dip varies from less than 

 20° to 80° or 85° (Figures 36 to 40). On the north side of the granodiorite a 









Figure 38. — Plunging contact surface between intrusive granodiorite (on the right) 

 and Pasayten formation (on the left). Drawn from a photograph taken on the north 

 side of the Castle Peak stock, near the point " C", Figure 35. View looking east. Con- 

 tact shown by heavy line in middle of view. Granodiorite on right of the line, which 

 represents 1,700 feet of depth at nearer ridge. Contact also located in the background, 

 with broken line. 



section of the domed roof of the magma chamber still remains (Figure 40). It 

 is noteworthy that a well developed system of rifts or master joints in the 

 granodiorite seems, with its low dip, to be arranged parallel to the north sloping 

 roof, as if due to the contraction of the igneous rock on losing heat upward by 

 conduction. 



25a— vol. ii— 32 



