MESOZOIC OF SOUTHWESTERN OREGON 527 



for many miles. The lowest horizon for a number of miles is a 

 conglomerate, and the range of fossils indicates that the complete 

 series is represented up to the top of the Horsetown horizon. Diller 

 has estimated the thickness at about 6,000 feet, and the writer's 

 observations confirm this figure as a good approximation. 



The lower division. — Unfortunately, the lower series is so broken, 

 and its stratigraphy so obscure, that it was not found practicable to 

 measure its thickness, but the fact that it has been more strongly 

 disturbed than the upper division, and yet covers larger areas in 

 which it has been deeply dissected by streams without exposing the 

 underlying rocks, would seem to indicate that it is at least as thick 

 as, and probably thicker than, the upper group. 



PALEONTOLOGIC CHARACTERS 



The upper division. — The upper group has yielded a considerable 

 amount of. fossil material. Its lowest beds are characterized by the 

 presence of Aucella piochi, the characteristic fossil of the lower 

 Knoxville in California, and, as higher beds are examined, they 

 show, in order, fossils of the upper Knoxville and of the Horsetown, 

 as already described on p. 519. In fact, all of the fossils described 

 in the texts of the Roseburg and of the Port Orford folios (no Mesozoic 

 fossils were found in the Coos Bay quadrangle) as characteristic of 

 the Myrtle formation, indeed all fossils described as occurring in 

 the Myrtle formation except the radiolaria of the cherts and the 

 imperfect shells in the Whitsett limestones, occur in the upper group 

 of formations. 



The lower division. — The lower or semi-metamorphic series is 

 almost destitute of fossils, except the minute remains of radiolaria, 

 etc., in the cherts and limestones, and these do not definitely indicate 

 the horizon. In the limestone lentils Diller has found a "few, gen- 

 erally imperfect fossils" in which Mr. T. W. Stanton has recognized 

 Opts californica and "a species of Hoplites, either closely related to 

 or identical with Hoplites dilleri." As there is apparently some doubt 

 about the determinations, and as the range of the above fossils is not 

 known, it cannot be said that they indicate the age of these beds with 

 any definiteness, although we may accept them as showing that the 

 limestones are probably Jurassic or Lower Cretaceous. The position 

 of this series, however, stratigraphically below the base of the upper 



