MESOZOIC OF SOUTHWESTERN OREGON 521 



Orford area, none having been yet reported for the other two quad- 

 rangles, we may consider the Myrtle formation of Diller, as defined 

 by its original limits, to include those strata from the basal Knoxville 

 to the uppermost Horsetown, that is, to be equivalent to the Shasta 

 group of the California Cretaceous. 



OUTLINE OF MESOZOIC AND RELATED HISTORY 



In the text accompanying the Port Orford folio Diller gives a 

 general sketch of the events of the geological history of that and 

 related areas, and, as the most recent summary of our knowledge of 

 this region, it may be well to consider in outline the chief events 

 there given which relate to the Mesozoic history, its beginning and 

 end. Arranged in historical order, these are: 



1. Ancient sea in which Colebrooke schists were 1 Pre-Cretaceous. 

 deposited J Pre-Devonian ? 



2. Interval between Colebrooke deposition and that! T . j urass j c : nr i ]f i; n p- 

 of the "Lower Cretaceous Myrtle formation." J - 



2. a (Upper Jurassic deposition indicated, the Kla-1 x , T ura ssic 

 math Mountains probably submerged.) J J 



3. Upraising of Klamath region; coast moved west- -> p , T 

 ward beyond present position (probably to mar- I p iyr , +1 



gin of continental plateau); important mountain- | /p xr '.,, -> 

 forming epoch. 



4. Subsidence, the sea advancing inland until most 1 T r + 



n r x7-i .1 tvt . ■ ii .Lower cretaceous 



or all of Klamath Mountains were covered, and 



waves swept the foot of the Blue Mountains in 

 eastern Oregon, and the Sierra Nevada of Cali- 

 fornia. 



> (Myrtle) period. 

 (Shasta.) 

 Continued into Chico. 



5. Folding, crushing, intrusion of igneous rocks,-, 



and whole raised above the sea; extensive ero- 1 Chico in part? and Cre- 

 sion, the Chico being removed except one or two f taceous-Eocene interval, 

 small patches. 



6. Subsidence and marine deposition. Eocene. 



THE HETEROGENEITY OF THE MYRTLE FORMATION 



It will be noted that in the above outline the Myrtle formation is 

 considered as representing a period of continuous marine sedimen- 

 tation, and the igneous intrusives with which it is so abundantly 

 supplied are considered post-Myrtle, indeed post-Chico; that is, 

 post-Cretaceous. And this is the idea which underlies all the descrip- 

 tions of the Myrtle, both of this and the other quadrangles. The 

 results of the writer's field studies, however, are to the effect that 



