244 



j. F. XEWSOM CLASTIC DIKES 



known. The top of the mass conforms with the overljnng shale, but its 

 bottom is very irregular, expanding down in one place to a mass about 

 7 feet thick, beneath Avhich the shale beds l)end very slightly, forming a 

 local sjniclinal fold. From the lower side of this mass there are branches 

 which either rejoin the parent mass or thin out and disappear in the 

 underlying shale. Figure 14 shows the conditions at this point. 



At 37 a number of very thin bituminous sand dikes are exposed on 

 the wave-washed sea cliff. They range in thickness from i inch to IJ 

 inches. The}^ branch and coalesce; their strike is north 15 degrees east. 

 Fifteen hundred feet north w^est of the mouth of Majors creek, dike 38 

 outcrops (figure 1, plate 26.) This intrusion is exposed on the wave- 

 washed shale bench for 150 feet and is from 6 inches to more than a foot 

 thick. It is of hard, dark gray, fine grained sandstone. It is almost ver- 

 tical and reaches to the top of the sea cliff, and owing to its hardness 



projects from the sur- 

 rounding shales. The 

 sandstone is much 

 fractured and con- 

 tains great numbers 

 of false veinlets which 

 are harder than the 

 rest of the dikes. 

 Many of these appar- 

 ent veinlets are com- 

 posed of sand, the 

 grains of which have 

 been cemented by calcium carbonate. They have probably been formed 

 by lime-bearing water passing along fractures and depositing its lime in 

 the sand on either side. While the sand has the dark color of the bitum- 

 inized dikes of this locality, it is not charged with bitumen where 

 exposed. 



At 39, just south of the mouth of Laguna creek, a group of small, 

 branching, highly bituminized dikes is exposed. These intrusions are 

 faulted laterally near the top of the sea cliff, which is about 40 feet high. 

 In thickness they vary from a fraction of an inch to 10 inches ; notwith- 

 standing their small thickness they contain many inclusions of diatom 

 shale. 



The manner in which these intrusions send off branches which re- 

 unite, or thin out to mere films and disappear, is shown in figure 1, plate 

 28. In hardness they do not var}^ greatl}^ from the adjacent shales. 



At 40, just west of the mouth of Laguna creek, is a 10-inch dike of 

 soft sandstone. 'J'his intrusion offers an eas}^ point of attack for the 







Lc::::n.^:iifiATOM shale ■ — 



71 



■iMHJl^^ 



^. 





— ~ ~^~^'^"- — ^^"^TJTATOM SHAT.F '-- 





-^^IZ^r^,^<^:^:^^^^>::^ Z^ 



JOft 



Figure li.—^Iass of Bituminous Sandstone. 



This sandstone conforms in part to the shale beds near the mouth 

 of Majors creek. 



