540 GEORGE DAVIS LOUDERBACK 



AREAL DISTRIBUTION IN THE REGION STUDIED 



General method of determination. — The writer has determined the 

 distribution of the Dillard and the Myrtle over considerable areas 

 by actual field studies. In certain areas not visited, but which have 

 been mapped and described in the various folios, the relative distri- 

 bution may be approximately arrived at from an interpretation of 

 the mapping and descriptions by means of the characteristic features 

 which have been described above for each set of formations. The 

 exposition of these field relations is probably best made by consider- 

 ing the folios seriatim as published by the Geological Survey, and 

 indicating which of the areas there mapped as the " Myrtle formation" 

 are occupied by the formations of the Dillard series, and which by 

 the members of the Myrtle group, at the same time referring to their 

 occurrence in neighboring, but as yet unmapped, areas. 



THE INTERIOR QUADRANGLES 



General distribution in Rosebnrg quadrangle. — If one turn to the 

 "Historical Geology Sheet" of the Roseburg folio he will see that 

 these formations occur only in the southern half of the quadrangle. 

 The sedimentary rocks occur as three main areas, elongated in a 

 northeast-southwest direction. The northernmost or largest may 

 be called the Dillard area from the village of that name situated in 

 its midst; the second may be referred to as the Myrtle Creek area, 

 and the southernmost, in the southeast corner of the quadrangle, as 

 the Days Creek area, for obvious reasons. There are also a number 

 of small disconnected patches. 



The Dillard area. — A large part of the Dillard area was studied 

 by the writer, with the result that everywhere formations character- 

 istic 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 infoldings 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 characteristic 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. 



