414 Diller — Mesozoic Sediments of Southwestern Oregon. 



as the Dillard area. The lentils of limestone (Whitsett) and 

 the larger masses of radiolariau chert, amphibole schist, and 

 igneous rocks within the area are separately outlined and the 

 great predominance of the other sediments is apparent at a 

 glance. 



Hocks considered. — Igneous rocks play a very important 

 role in the geologic records of southwestern Oregon. Many of 

 the rocks are of types found elsewhere in the Klamath Moun- 

 tains at various horizons in the Paleozoic and Mesozoic. Since 

 their ages are determined by reference to associated sedimen- 

 tary rocks they will not be considered in this paper, which will 

 be devoted to the consideration of the sedimentary rocks only. 



Different mews. — The Myrtle formation of the Dillard area 

 was described in the Roseburg folio as Cretaceous and 

 regarded as having its equivalence in the Knoxville and 

 Horsetown of the Shasta group in California. Mr. Louder- 

 back designated the rocks of the same area as the " Dillard 

 series," and regarded them as stratigraphically below and older 

 than the Knoxville and equivalent to the Franciscan of 

 California. 



Locality of Louderback s observations. — Mr. Louderback 

 states (p. 540) that " a large part of the Dillard area was 

 studied by the writer, with the result that everywhere forma- 

 tions characteristic of the Dillard series were found, while no 

 representative of the Myrtle group was recognized. It is 

 probable that this whole area belongs to the lower series, 

 although a more complete study may show subordinate patches 

 or infoklings of the lower members of the Myrtle group. All 

 of the members of the sedimentary series, all of the main types 

 of igneous rocks, and the peculiar schists, described as charac- 

 teristic of the Dillard series, occur within this area. The 

 Whitsett foraminiferal limestone lentils crop out at intervals 

 from about four miles directly east of Dillard to the northeast 

 extremity of the area." 



Expecting to have an opportunity to re-examine the " Dil- 

 lard area" in connection with the survey of the Riddles quad- 

 rangle, which adjoins the Roseburg upon the south, I wrote 

 to Mr. Louderback, enclosing a geological map of the Hose- 

 burg quadrangle and asked him to indicate by shading or 

 otherwise " the large part of the Dillard area" he had studied, 

 so that in the field I would have a lithological standard of 

 comparison in endeavoring to discriminate between his " Dil- 

 lard series " and " Myrtle group." In reply he stated : " I 

 examined the country along all of the roads of that area north- 

 east of the Umpqua River, and furthermore I visited those 

 areas mapped as amphibole schist and as limestone which lie 

 off the roads. To the southwest of the river I went over the 



