The Geologic Map 95 



formations on the slope of the Sierra Range are remnants of 

 the ancient roof. Where the roof rocks have been removed 

 the granitic bed-rock of the batholith is now exposed at the 

 surface, and these rocks are shown on the geologic map as 

 plutonic rocks. 



A geologic map is thus seen to be a somewhat complicated 

 affair, but it shows the formations that lie at the surface in any 

 locality. The geologic section at any given place shows what 

 formations extend from the surface downward, and may, but 

 does not always, extend to the ultimate basement or foundation 

 rocks. A generalized or ideal geologic section would show all 

 the formations of the earth from the soils and alluvium of the 

 present down to the ultimate basement, the Archaean granite 

 rocks of the foundation of the earth. As has been stated, these 

 formations are not all known in any one place, but by general- 

 izing from a great number of observations in widely distributed 

 areas the perfect or ideal geologic section of the crust of the 

 earth may be made. 



