246 



J. F. XEWSOM — CLASTIC DIKES 



the bottom of the sea cliff, which is about 50 feet high. At its east end 

 the mass cuts the shales to the top of the cliff in a chimney-shaped mass 

 40 feet across. Throughout this mass of soft sand are irregular wavy 

 bands indicating flow structure. The peculiar wavy banded structure 

 is shown in figure 16, which is from a photograph of the eastern end of 

 the mass, showing its thickest part and also the chimney-like portion. 

 The diatom shale immediately east of the dike dips 15 degrees south, 

 75 degrees west, while that at the west end of the mass dips 10 degrees 

 south, 15 degrees east. 



The sandstone of this intrusion is practicall}^ free from the odor of 

 bitumen. The line of contact between the adjacent overljdng shale and 



the sand at the west end of the exposure 

 is irregular. Intrusions of shale occur 

 in the sand mass near the west end of 

 the exposure. 



At 50 is a dike of soft gray sand vary- 

 ing in thickness from 10 inches to 2 

 feet. This intrusion is exposed for a 

 hundred feet near the bottom of the 

 sea cliff. At its two ends it cuts the 

 shale beds at angles varjing from 10 



"= = to 30 degrees, while at its middle it 



conforms to the shale beds. This dike 

 is within 100 feet of the large Respini 



^ ■ ^ Creek dike (51). from which it is prob- 



abl}^ an offshoot. 



The Respini Creek dike (51, figure 

 10, and figure 2, plate 28), the largest 

 of the Santa Cruz intrusions, has an exposed width of 600 feet along the 

 sea-clifif immediately southeast of the mouth of Respini creek, and ex- 

 tends one-fourth of a mile inland. It is composed of rather fine grained, 

 yellowish brown and gray sand, free from bitumen. The sandstone 

 varies from soft friable material, from which the cementing material, if 

 ever present, has been leached, to hard compact stone. The surface of 

 the intrusion is much pitted by the action of the waves and by the 

 weather and is broken by many joint planes. At places it presents 

 a peculiar wavy banded structure, some of the bands being harder than 

 others. The hardness of some of the thin laj'ei'S that resist the action of 

 the weather is apparently due to iron oxide as a cementing material. 

 At other places there are groups of vertical columns of hard, gray, 

 jointed sandstone, extending to the top of the cliff. Adjacent to these 

 columns, of which there are many groups, the sandstone of the dike is 



Figure \b.— Diagram of Dike at US. 



