MESOZOIC OF SOUTHWESTERN OREGON 543 



of the same nature, about three-quarters of a square mile in area, 

 entirely inclosed in the serpentine, and apparently torn from the main 

 area by the act of serpentine intrusion. Another small area lies 

 entirely in the "metagabbro" along the Umpqua River (near the 

 railroad), and is also associated with serpentine dikes not shown on 

 the map. 



All of these smaller areas are composed of Dillard sandstone, etc., 

 which show their characteristics very distinctly, and are, in general, 

 considerably altered. The form of each of these areas is rather long 

 and narrow, and it can be distinctly seen in the field that they do not 

 merely lie on the intrusives, but in them as included or partially sub- 

 merged masses. 



Contrast between close-lying areas of Myrtle and Dillard. — The 

 strong contrast and abrupt change (i. e., not gradational) between 

 the Myrtle and the Dillard can be well observed on ascending the 

 ridge a few miles southwest of Dodson Mountain, going up from 

 Bilger Creek so as to reach the Dillard areas as close to the Myrtle 

 as possible. After leaving the Myrtle shales, one passes onto the 

 basal conglomerates which are regularly bedded with a very uniform 

 strike for miles, along the higher flanks of the r. ^e. Leaving these 

 conglomerates, one passes onto the serpentine, and then shortly onto 

 the disconnected area of Dillard. This shows no trace of con- 

 glomerate, but is chiefly of hard gray sandstone, well cemented, and 

 not infrequently traversed by quartz veins and stringers. The strike 

 is irregular. At one point near the border, it is perpendicular to the 

 regular strike of the Myrtle, which is only some 200 or 300 yards distant 

 across the serpentine. The characters of the Dillard would seem to 

 be largely dependent on its intrusion, while in the Myrtle nothing that 

 could be definitely referred to intrusive action was observed. 



To the south, in the vicinity of Canyonville, sedimentary rocks of 

 the Dillard group are found on the southeast side of the Myrtle 

 Creek syncline. Their extent was not determined, nor their con- 

 tact with the Myrtle studied. 



The Days Creek area. — The writer did not visit the Days Creek 

 area, but from the statement in the text of the Roseburg folio, which 

 refers to the Horsetown horizon, that "fossils of this horizon have 

 been found .... throughout the area along Days Creek," we may 

 infer that it is entirely Myrtle, perhaps all Upper Myrtle. 



