MESOZOIC OF SOUTHWESTERN OREGON 517 



raphy and history of the region were recognized, and a closer corre- 

 lation between the geological conditions and sequence in southwestern 

 Oregon, and those of the California Coast Ranges, made possible. To 

 set forth these general results is the purpose of the present paper. 



HISTORICAL 



The region under discussion lies in southwestern Oregon, and is 

 included from east to west between the western foothills of the Cascade 

 Range (long. 123 west), and the Pacific Ocean (about 124 20' to 

 124 30' west); and from north to south between the latitude of 

 Roseburg or the head of Coos Bay (about lat. 43 15' north), and 

 the Klamath 1 Mountains (about 42 30' north). This field has 

 been studied by few geologists. Dana and later Newberry, in their 

 exploration work in the early days, saw but little of the country, and 

 were hardly in position to arrive at any definite conclusions as to 

 even the major events in the geological history of the region. Mr. 

 G. F. Becker, 2 about 1890, studied some of this country in the vicinity 

 of Riddles in conjunction with Mr. W. Q. Brown, and arrived at 

 certain conclusions that were important in extending the knowledge 

 of the Pacific coast Cretaceous. It is to Mr. J. S. Diller, however, 

 that we owe by far the greater part of our present knowledge of 

 southwestern Oregon. He has spent a number of years in the 

 investigation and mapping of considerable areas, and his studies 

 have covered all parts of the region outlined above. His general 

 results are presented most systematically and with the greatest detail 

 in the texts accompanying the Roseburg, Coos Bay, and Port Orford 

 folios 3 of the Geologic Atlas of the United States, although certain 

 features are more particularly treated in various memoirs, a number 

 of which will be referred to in the body of this paper. 



AREAS STUDIED 



The index map, page 518, shows the relative positions of the 

 three geologically mapped quadrangles of southwestern Oregon — 

 the Coos Bay and Port Orford lying in contact on the coast, and 



1 For use of this term see p. 552. 



2 Bulletin of the Geological Society of America, Vol. II (1801), pp. 201-6. 



3 U. S. Geological Survey, Geologic Atlas of the United States, Folios Nos. 49 

 (1898), 73 (1901), and 89 (1903). 



