MESOZOIC OF SOUTHWESTERN OREGON 535 



folding. No trace of contact phenomena was observed in the soft 

 shales or the conglomerates, and these exposures appear to be due 

 to faulting along the line of the structural axis, bringing some of the 

 "rim" rock to the surface. 



The Myrtle conglomerate. — In this area the lowest beds carry 

 fossils that are characteristic of the base of the Myrtle and a heavy 

 basal conglomerate rests on the surrounding igneous rocks. This 

 conglomerate is evidently the result of long-continued grinding 

 together of the component rock fragments, for the material of the 

 Dillard formation has been worked over to such an extent that the 

 rock types appear in no wise in proportion to their relative areal 

 abundance, but apparently mainly in proportion to their relative 

 resistance to abrasion. 



The cherts are the most abundant pebbles, the dacites (and 

 andesites) next. In some localities the latter are more abundant 

 than the former. They show the same textures, mineral composition, 

 range of variation of characters, and general appearance as the 

 Dillard dacites and andesites, and are undoubtedly the same. The 

 characteristic Dillard sandstone is but sparingly present, as also are 

 the types of the granular basic rocks. Some characteristic quartz- 

 diorite pebbles were found, but greenstone pebbles are exceedingly 

 rare, and glaucophane schist, serpentine, and shale were not found 

 at all. Of these it may be remarked that the greenstones are usually 

 badly decomposed and crushed; the schists occur only in small 

 quantity and are readily disintegrated on account of their fissility; 

 and the serpentine and shales are more or less soft and generally 

 friable. 



Other evidence. — -The relationships of the above-described igne- 

 ous rocks are in general so evident that even without the testimony 

 of the Myrtle conglomerate they would be referred to pre-Myrtle 

 eruptions. The serpentines, however, are rather noncommittal. 

 They lie on the Myrtle contact for several miles, and yet are unrep- 

 resented in the basal conglomerate. But their absence from this 

 conglomerate appears to be satisfactorily accounted for by the con- 

 siderations presented in the last paragraph. They are here referred 

 to the pre-Myrtle because they occur so frequently as dikes and 

 masses throughout the Dillard, while they are found only on the 



