U2 



.1. S. I'll LEE A.NDSTONE 1'IK I S. 



for fossils, in the belief thai the rock from which they were derived was 



ajularly interstratified with the Cretaceous shales. Near by I discovered 



an excellent exposure of a vertical dike cutting through the bank of tilted 



shales from top to bottom, in plain view for a distance of 60 feet. When I 



i' ached tin- dike and found it to he composed of sandstone, tin- same I hail 



amined for fossils, my interest was thoroughly aroused. A Bandstone dike 



tned a paradox. Further Bearcb in that region brought other dikes of 



the same nature to light, hut the puzzle was oot investigated until Last 



summer, when, with the aid «»i' Mr. .J. Stanley-Brown, a geologic ma]) of the 



district was prepared. 



Distribution of the Sandstone Dikes in Northern California. 



Genera/ h'* /<tti<>ns. — The position of the region containing the dikes is in- 

 dicated upon the accompanying map, figure l,by the small rectangular area 

 bounded by heavy lines near the center of the map. The heavy line within 

 the rectangle shows the general direction of the dikes. 



i.i 1 '.• U \p of Northi i ' \ia. 



The rectangular nrcn nonr (ho center shows the position >>( the Bandstone dike district, trhioh i- 

 represented upon ■ larger scale In ti^iir" 2. 



\V< -i "i |;, ,i Bluff, California, there La a wide and comparatively low pass 

 through a pari of the Coast Range between the peaks of Yallo Bally and 

 Bully Choop to Hay fork of Trinity river. The eastern dope of the pass is 



drained by the converging tributaries <'f Cottonw 1 creek, which unite to 



form the main stream twenty milee west of the Sacramento. 



Across :i base level of erosion, formed by the planing off of the tup of the 

 Cretaceous shales and sandstones, these streams have cut valleys considerably 



