Diller — Mesozoic Sediments of Southwestern Oregon. 411 



the southeast, as if the Jurassic passed beneath the Paleozoic 

 as a result of au overturn. However, the structure has not 

 yet been resolved and the faunal differences between the 

 Dothan and the Galice are not sufficiently great for age dis- 

 tinction. 



Myrtle Formation ( Cretaceous). 



Characterization. — The Myrtle formation is a succession of 

 shales, sandstones and conglomerates in which the alternating 

 shales and sandstones, often thin-bedded, are of approximately 

 the same volume but the conglomerates, generally fine, are of 

 much smaller mass. Lentils of chert and limestone occur 

 locally and the whole assemblage of beds is characterized by 

 such a lower Cretaceous fauna as demonstrates its essential 

 equivalence to the Shasta series of California. 



Litfiiftcation. — The greater portion of the rocks of this for- 

 mation are somewhat less firmly lithified than the majority of 

 those belonging to the Galice and Dothan formations, but this 

 is not the case everywhere. In the Myrtle, carbonate of lime 

 as cementing material and in veinlets is widely distributed 

 though siliceous cement and quartz veinlets are common in 

 some areas. In the two Jurassic formations silica is the more 

 common and widely distributed cementing material and quartz 

 veinlets are locally abundant. Carbonate of lime is often pres- 

 ent in them, but in both cement and veinlets it plays a much 

 less extensive role than silica. 



On lithological grounds, therefore, the Myrtle and Dothan 

 are not always easily distinguished. The higher degree and 

 more extensive silicification of the Dothan affords presumptive 

 evidence, but it is only by means of fossils or definite strati-' 

 graphic data having reference to fossiliferous horizons that af- 

 fords a satisfactory basis for separating the Dothan and Myrtle 

 in the field. 



Distribution. — The Myrtle formation lies north and north- 

 west of the Dothan. Its largest area is along the coast about 

 the mouth of Rogue River and as far north as the Sixes, where 

 it passes beneath Eocene. This area mapped in the Port 

 Orforcl folio as Myrtle certainly contains some Jurassic rocks 

 for they have locally yielded Aucella erringtoni in the stream 

 gravel of Johnson Creek, but as the fossils could not be found 

 in place, and the rocks thus distinguished from similar rocks 

 containing Knoxville fossils in the same region, they could not 

 be mapped separately. 



East of the Coast Range beyond the Eocene the Myrtle 

 formation reappears along Myrtle Creek from which the for- 

 mation was named and also a short distance farther northwest 

 about the post-office of Dillard. All three areas are indicated 



