76 Adventures in Scenery 



5 and 6 miles. That the Knoxville beds attain so considerable a 

 thickness in the region of the Coast Ranges indicates that the 

 sea floor continued to subside steadily during Knoxville time. 

 The Knoxville subsidence was widespread, and is spoken of as 

 an epeirogenic movement, that is, a movement of the earth's 

 crust that embraces a wide region. 



The long-continued deposition of muds (forming shale) 

 in the lagoons and marshes of the shallow Knoxville sea was 

 interrupted by an orogenic movement (mountain building) 

 which lifted the coasts of the Cretaceous sea but did not greatly 

 affect the broad sea bottom. The result was the quickening of 

 the streams that flowed into the sea, and coarse sediments were 

 deposited in deltas on the shores, and sands carried out to sea. 

 Thus a changed condition was brought about and a new series 

 of sediments deposited. This change marks the end of the 

 Lower Cretaceous, and the beginning of the Upper Cretaceous 

 (Chico) series of formations, and thus marks the break in the 

 geologic record between the Lower and Upper Cretaceous 

 periods. With this disturbance the present region of the Coast 

 Ranges became dry land. 



Great Changes Mark Close of 

 Mesozoic Era 



The close of the Cretaceous period marks the end of the 

 great Mesozoic era and the beginning of Tertiary. Great 

 changes in sea and land throughout the continent occurred at 

 this time. It was at this time that the great ranges of the Rocky 

 Mountain system came into being. The ushering in of the Ter- 

 tiary era was marked by no violent mountain-building move- 

 ments in the Pacific Coast region, but there was marked uplift 

 which brought the floor of the sea to dry land. The sea was 

 shut off from much of California by the uprising of the Coast 

 Ranges. There remained a great sound or arm of the ocean 

 where is now the Great Valley of California. A long interval 

 of erosion ensued. The region of the Sierra Nevada was up- 



