520 GEORGE DAVIS LOUDERBACK 



It would appear, then, that the "Myrtle formation" as originally 

 described has very definite limits, running from the base of the 

 Knoxville to the top of the Horsetown — an interval named in Cali- 

 fornia the Shasta group by Whitney as early as 1869. 



In 1 901, Diller referred the pre-Eocene rocks of the southern 

 part of the Coos Bay quadrangle to the Myrtle formation, although 

 no fossils were found in them within the limits of the quadrangle. 

 The nearest fossil localities are some miles south of the southern 

 boundary, and indicate a Knoxville age. Cherts with the same 

 relationships as those of the Roseburg quadrangle are here referred 

 doubtfully to the Cretaceous, but they are not included in the Myrtle 

 formation. 



In the Port Orford folio (1903) considerable areas are mapped as 

 Myrtle. This term, in general, has the same significance as in the 

 former publications, and is treated under the Cretaceous. The 

 occurrence of some small areas of Jurassic within the areas mapped 

 as Myrtle is indicated by fossils found in float material, but their 

 occurrence in situ could not be determined. There were also some 

 small patches of rock found which contain Chico (Upper Cretaceous) 

 fossils. Almost the whole of the area mapped as Myrtle, however, 

 is described as corresponding to the Myrtle of the original localities 

 in the Roseburg quadrangle, that is, to the Shasta group of California. 

 The wording of some parts of the text, however, make it doubtful 

 whether Diller intended to retain the same limits for the Myrtle 

 formation as was determined in the type locality, or whether he 

 would extend the term to include whatever Upper Cretaceous (Chico) 

 were present, and make it equivalent to the Shasta- Chico series of 

 California. If such had been the intention, it might be expected 

 that the term "Myrtle series" would have been used as comprehend- 

 ing so many groups of formations. It may be added that the cherts 

 of the Port Orford quadrangles, which have the same geological 

 relations as those in the other two quadrangles, are here included in 

 the lower (or Knoxville) part of the Myrtle, so that even with the 

 original limits the term "formation" seems very inadequate, and is 

 likely to produce an incorrect conception of the complexity of the 

 Myrtle. 



As the Chico areas are but one or two small spots in the Port 



