88 Adventures in Scenery 



an unconformity, means that there is a "lost interval" here in 

 the succession of formations. It may mean that this place was 

 not sea bottom but was a land surface at this period of the 

 earth's history, and that no sediments were deposited. Or it 

 may mean that this region was elevated above sea level after 

 deposition of sediments and that these were removed by erosion, 

 and that later the land sank and was covered by the sea and 

 another formation deposited. In either case there is a break 

 in the geologic record. It means a "lost interval" for this 

 locality. 



Region East of Berkeley 



In figure 24 the areal geology of a portion of the Conrad 

 quadrangle lying east of San Francisco Bay, immediately east of 

 Berkeley, is shown. Cross sections of the formations along the 

 lines A B, and C D are shown in figures 25 and 26. The 

 surface of the land is that of a rolling hilly plain. The forma- 

 tions at the surface are shown on the map and designated by 

 numbers. The cross sections show that the rocks have been 

 much folded, bent and faulted by upheavals. At the surface 

 are the worn and eroded outcropping edges of the disturbed 

 formations. 



Rock formations in California have been upheaved, bent, 

 and folded since they were deposited, and irregularities appear 

 in cross sections. Where an uplifting of the rocks has occurred 

 and the crown or top of a fold or arch has been eroded, the ends 

 of the bent strata will be exposed at the sides and the older 

 formation will appear in the center. 



In the cross section, figure 25, four geologic formations 

 occur at the surface in a distance of about 3 miles. The 

 Briones sandstone (12) has been uplifted and the top of the 

 arch or fold has been removed by erosion. The younger rocks 

 of the San Pablo formation (14) dip away from the uplifted 

 Briones, and the two formations are separated by an uncon- 

 formity, showing that an interval elapsed after the Briones 



