412 Ditter — Mesozoic Sediments of Southwestern Oregon. 



upon the Geological Map of Xorth America and are shown 

 in detail in the Roseburg, Coos Bay and Port Orford folios, 

 where a more extended account of the Myrtle formation may 

 be found. 



Relation of the Myrtle formation to the Dothan. — The 

 actual contact of the Knoxville (Cretaceous) and the Dothan 

 (Jurassic) has not been observed though it has been followed 

 throughout the greater part of a distance of 50 miles and 

 mapped in detail for nearly 30 miles. From Rogue River 

 below the mouth of Mule Creek northeast to West Fork the 

 Knoxville follows the border of the Dothan series, but near 

 that point it turns abruptly east by way of Xichols Station to 

 Canyon ville, unconformable overlapping the broad belt of 

 Dothan. Although the contact could not be found exposed, 

 the strike of the Dothan carries it directly beneath the Knox- 

 ville ; it is for the most part more disturbed and more firmly 

 lithified than the Knoxville and there can be no reasonable 

 doubt that the unconformity is generally great. The Dothan 

 and Knoxville where exposed within a few rods of each other 

 are generally in strong contrast, the Knoxville strata having 

 calcareous veins and cement while those of the Dothan are sili- 

 ceous bespeaking a decided discordance, but this is not always 

 true, for the Dothan, as near Nichols, well characterized by 

 Aueella erringtoni, is locally calcareous and the Knoxville, in 

 places equally well characterized, is locally siliceous. 



Plant beds. — Plant beds containing a flora which according 

 to Ward,* Fontaine and Knowlton has a decidedly Jurassic 

 facies, occur in southwestern Oregon and northern California. 

 In Oregon and more especially at Big Bar, CaL, some of the 

 plants of Jurassic facies are clearly associated with shells 

 which are regarded as characteristic of the Knoxville, but near 

 Oroville, CaL, the plant beds contain an assemblage of shells 

 which Dr. Stanton reports as having " a decided Jurassic 

 aspect," in his opinion " older than the aucella-bearing Mariposa 

 formation.- ' The plant beds with " Jurassic flora " will be con- 

 sidered in a separate paper. 



The Dillard Series of Louderback. 

 Introduction. 



Louderback '«§ general results. — "'' The Mesozoic of South- 

 western Oregon" is the title of a paper! in which Prof. G. D. 

 Louderback considers particularly the Myrtle formation of the 

 Roseburg, Coos Bay and Port Orford folios. The results of 

 bis studies, to use his own language (p. 521), " are to the effect 



*20tk Ann. Kept., pt. 2, pp. 368-377, and Monograph LVIII. 



f Journal of Geology, vol. xiii, No. 6, pp. 514-555, Sept. -Oct., 1905. 



