418 Diller — Mesozoic Sediments of Southwestern Oregon. 



Mesozoic fossils collected during the season in Douglas County. 

 He says : 



"In the Douglas County area the discrimination between the 

 Jurassic and Cretaceous rests on the same slender basis as in 

 the case of previous collections from the same region, that is, 

 most of the localities in question contain no determinable fos- 

 sils except Aucella, and when these are marked w T ith numerous, 

 distinct, radiating striae they are referred to the Jurassic 

 species Aucella erringtoni. The Cretaceous species Aucella 

 piochii has very nearly the same form, but lacsk the radiating 

 striae. 



It is evident, therefore, that the paleontologic separation of 

 Jurassic and Cretaceous cannot be very positively made, espec- 

 ially when the surface features of the fossils are not very well 

 preserved. It is true, however, that all of the specimens in 

 this collection that can be referred to A. erringtoni came from 

 the area that had previously been determined as Jurassic, and 

 was so classified in Mr. Diller's list. This species was recog- 

 nized in the lots from Thompson Creek, Table Creek, O' Shea 

 Creek, and doubtfully in those from the South Fork of Beal 

 Creek. The other lots from the supposed Jurassic area usually 

 contain only fragmentary sjDecimens of Aucella that cannot 

 be specifically determined, or, in a few cases, some other fossil 

 which is not diagnostic." 



" The lots that were classified in the field as Cretaceous 

 (including those of the Dillard area) apparently all belong to 

 that system, although a few of them do not contain enough to 

 distinguish between Jurassic and Cretaceous. " 



Quarts veining. — A considerable portion of the rocks of the 

 Dillard area contain veinlets of quartz and in some cases the 

 veinlets are abundant, though their distribution is very irreg- 

 ular. They occur most frequently in compact gray sandstone 

 and are mere films, a small fraction of an inch in thickness and 

 but a few inches in extent. Some irregular masses occur of 

 a few feet in length. 



A good exposure of this siliceous sandstone occurs in the 

 immediate vicinity of the limestone lentil at the Marble Works 

 in the eastern part of Sec. 19, T. 27, R. 4, and in the hills 

 within 2 miles to the westward, where some of the beds con- 

 taining quartz veins have calcareous cement and in others such 

 veins are entirely absent. 



Southwest of the Uinpqua River among the rocks of the 

 Dillard area a somewhat larger proportion is veined with quartz 

 generally associated with those of calcite. Where quartz vein- 

 lets are most abundant calcite is often wanting. Towards the 

 heads of Kent and Rice creeks, such rocks contain Aucella 

 crassicollis, affording definite evidence of their Knoxville age, 



