J. S. Diller — Bragdon Formation. 381 



type area."* As shown upon the accompanying map, it is 

 roughly pear-shaped, constricted in the small part with the 

 longer axis running nearly northeast and southwest. The big- 

 ger end lies near Trinity River from Lewiston to Trinity Cen- 

 ter, while the smaller end is trenched by the Sacramento from 

 Portugese Flat to Morley, and the long broad stem runs north- 

 east from North Salt Creek to the McCloud, a total length of 

 fifty miles and maximum breadth of about twelve miles. The 

 borders are locally irregular and there are a few small outlying 

 masses of Bragdon, but in general this area is remarkable for 

 its continuity from the Trinity River to the McCloud without 

 interruption excepting a small area of Devonian on Little Sugar 

 Loaf Creek and small areas of volcanics on Clear Creek and Dog 

 Creek, as well as several long narrow masses, not shown on the 

 map, east of the Sacramento River. The smaller end of the 

 Bragdon area, including the stem lying east of the Sacramento, is 

 bordered on the one hand by the Carboniferous sediments and on 

 the other by those of Devonian age ; but west of the Sacramento, 

 excepting a small bit on Backbone Creek, the type area of the 

 Bragdon is everywhere bounded by igneous rocks, some vol- 

 canic, others plutonic. It is evident, I think, that the region of 

 greatest promise in studying the taxonomy of the Bragdon is 

 east of the Sacramento, where it comes in contact both above 

 and below with sediments whose horizon is well established by 

 an abundance of fossils. West of the Sacramento we are 

 adrift among a plexus of igneous rocks whose exact age in 

 most cases is not easily determined. 



Stratigraphy. — The Bragdon, composed as it is of thin beds, 

 lacks a definite rigid horizon to resist folding. It is easily 

 crumpled, giving a great variety of dips and strikes. In the 

 part of the area east of the Sacramento the dips are sometimes 

 vertical, but for the most part not over sixty degrees, often under 

 thirty and generally to the eastward, and agree fully with the 

 general position of the Jurassic, Triassic and definitely known 

 Carboniferous (McCloud and Baird), all of which lie to the 

 eastward and increase in age westward, suggesting that the 

 Bragdon is the oldest and lies beneath the Baird. This view 

 is strengthened by an examination of the eastern limit of the 

 Bragdon where it adjoins the Baird. The limit may be traced for 

 more than twenty-five miles parallel with the Baird and 

 McCloud limestone, within a mile or two west of the latter, 

 and is marked by the disappearance of the characteristic Brag- 

 don conglomerate. It must not be supposed that the same 

 bed of conglomerate can be traced continuously along the east- 

 ern edge of the Bragdon for twenty-five miles. The conglom- 

 erate is in thin lenticular beds with traceable continuity of 



* Am. Geol., vol. xxxiii, p. 251. 



Am. Jour. Sci. — Fourth Series, Vol. XIX, No. 113. — May, 1905. 

 26 



