TRANSGRESSION OF THE CRETACEOUS SEA. 215 



ward still less. In none of the sections, however, has the exact top of 

 the Cretaceous been seen. Since these beds are all marine and form one 

 continuous series of sediments, it follows, from their distribution, that 

 during their period of deposition the sea was transgressing what is now 

 the northern portion of California. 



That the sea was transgressing during the Cretaceous is clearly shown 

 also by the character of the Cretaceous sediments. Before the deposition 

 of the Shasta group the Klamath mountains, composed of Jurassic, Tri- 

 assic and Paleozoic rocks, more or less metamorphosed, had been dry 

 land, exposed to weathering for a sufficiently long time to allow the sec- 

 ular disintegration of a mass of surface rock to form the residuary 

 deposits which have become the sediments of the Shasta group. In 

 some cases the deposits of the Shasta group bearing fossils rest upon 

 the residuary deposits and rotten rock from which they were derived, 

 and the line of contact is not easily recognized. This is the case on the 

 southeastern border of the Klamath mountains, in Shasta county, Cali- 

 fornia, between Ono and Igo, where micaceous sandstone at the base of 

 the Shasta group so closely resembles the rotten diorite on which it rests 

 that until the presence or absence of fossils is determined one is in doubt 

 which rock he may be examining* 



Near at hand, too, by the present streams, there are coarse shore con- 

 glomerates, including the gravels of the Cretaceous streams which flowed 

 down from the Klamath mountains on the northwest into the ancient 

 bay of the Sacramento valley, and one is surprised to find some evidence 

 that the valleys of the embouching streams of early Cretaceous times 

 are still occupied by streams. This may be true to a very limited 

 extent, but it is noticeable in the upper tributaries of the North Fork of 

 Cottonwood creek near Ono. 



From this point the Cretaceous rocks extend westward, and the later 

 members of the series lap up over the Yallo Bally and Bully Choop 

 ridge, the main divide of the Klamath mountains, crossing to the' west- 

 ern slope, where they appear well characterized by fossils in Redding 

 creek basin of Trinity county. In all cases the Cretaceous sediments 

 immediately in contact with the metamorphic rocks are of local origin. 

 When they are coarse the contact is plain and the unconformity so well 

 pronounced as to be beyond question, but where the sediments are fine 

 there may appear to be a gradual transition from the older metamorphic 

 rocks to the Cretaceous. For reasons already given, however, I am hilly 

 convinced that in northern California and Oregon it is chiefly apparent 

 and rarely if ever real.f It would be expected that the unconformable 



*See observations by Dr Dawson in Geol. Survey of Canada, Rept. of Progress, 1877-78, p. luG B. 

 He describes the same sort of phenomena at the base of the Cretaceous on the Skagit 



t Incases where the Cretaceous strata have been metamorphosed a transition from the unaltered 

 to the altered portions without an intervening unconformity would be expected. 



