528 GEORGE DAVIS LOUDERBACK 



group, whose range is rather definitely determined by the contained 

 fossils, fixes its upper limit and places the whole series below the base 

 of the Knoxville — the zone of Aucella piochi — from which it is sepa- 

 rated, as will be shown later, by an unconformity. 



TERMS USED 



Definition of the Myrtle group. — In discussing and describing 

 further the characteristics of the two well-defined and distinctly 

 separable groups of formations, it would conduce to simplicity and 

 clearness to give them names. If we define the Myrtle in terms of 

 the stratigraphic limits set by Diller and determined by characteristic 

 fossils, as that continuous sequence of beds whose base is the zone 

 of the Aucella piochi, and whose summit corresponds to the topmost 

 beds of the Horsetown group, then the Myrtle corresponds exactly 

 to the upper group above described. It is proposed, therefore, to 

 use the name "Myrtle group" for the formations so described, and 

 this term is particularly appropriate, as a most simple and complete 

 development of the Myrtle group occurs along Myrtle Creek and 

 about the town of that name — Diller' s type locality. If it should 

 seem better to extend the limits of the Myrtle to include the Chico 

 equivalents, as is perhaps Diller's intention in the Port Orford area, 

 the term "Myrtle series" would seem more appropriate. 



The Dillard series. — For the lower series, which, while it has been 

 mapped as Myrtle, is entirely below the stratigraphic limits set for 

 that group, the name, "Dillard series" will be used, after a village, 

 on the railroad, situated in the midst of the largest area of this series 

 on the Roseburg quadrangle. This series has already been charac- 

 terized stratigraphically and lithologically, and will be more concisely 

 defined later. 



IGNEOUS AND METAMORPHIC ROCKS 



ASSOCIATED WITH DILLARD SERIES 



General characters. — The Dillard series is abundantly supplied 

 with igneous rocks which are found at frequent intervals, especially 

 in the areas of the coast quadrangles, cutting it irregularly in all 

 directions. Most of these rocks are quite different from the igneous 

 rocks of any of the later formations and are, indeed, characteristic 

 of the Dillard series. They are so varied and irregularly mixed, and 



