The Geological Story Briefly Told 67 



of the crust of the earth by great masses of molten granite. 

 The exact time in geological history when this great disturbance 

 occurred cannot with certainty be stated, but it is thought to 

 have been in early Jurassic time. It is of great importance to 

 observe that this great upheaval of molten rock was injected 

 into rocks which had been previously deposited as sediments on 

 sea bottoms. The age of these earlier sediments is not known. 

 They are, however, known to be very old. For anything we 

 know to the contrary they may date back to the ancient Al- 

 gonkian (latest period of the Archaean or Archaeozoic) . All 

 this goes to show the great age of the land of California. 



Very long ago this tremendous upheaval occurred. A vast 

 mass of molten rock was forced up from the depths of the earth. 

 This molten rock was not poured out upon the surface, but 

 welled up under and into the rock formations that had been 

 laid down in ancient seas, lifting them as a great roof to the 

 height of high mountain ranges. The culminating event of this 

 series of great earth disturbances was the upheaval of a high 

 mountain chain in the region of the Coast Range, and of a great 

 mountain range or chain of ranges in the region where the great 

 Sierra Nevada was later uplifted. 



Rocks Changed by Heat and Pressure 



The heat of the molten rocks changed the character of the 

 sedimentary rocks which were intruded and upheaved. The 

 heat of the molten granite was very great, and this combined 

 with the great pressure involved, resulted in the metamorphism 

 of the rocks. Thus sandstones were changed to quartzites; clay 

 rocks, such as shale, were transformed into slate and schists; 

 limestones were changed to crystalline marble. So great pres- 

 sure resulted in folding, bending, crumpling, and crushing of 

 the intruded rocks. 



It is difficult to conceive of so great disturbance. What we 

 now see is the crumpled, folded, crushed rocks, now eroded and 

 broken during the long lapse of time. These are the broken 



