384 J. jS. Diller — Bragdon Formation. 



cerning the age and structural relations of the Bully Hill volcan- 

 ics, all observers practically agree in placing them about the close 

 of the Paleozoic and the beginning of the Mesozoic, but as to 

 the age of the large area of volcanics southwest of Bully Hill, 

 along the Sacramento — the rocks which Mr. Hershey has called 

 his Clear Creek volcanic series, I have but recently come to a 

 definite conclusion. The generally complete absence of vol- 

 canic material in the typical Bragdon conglomerates, and also 

 the fact that much of the igneous material which appears in 

 the areas of "Clear Creek volcanics" cuts the Bragdon, for a 

 long time counterbalanced in my mind the contention of 

 Hershey that the Bragdon is younger than the " Clear Creek 

 volcanic series" and rests directly upon it. But the discovery 

 of andesitic and rhyolitic material like that of the Clear Creek 

 series in certain Bragdon conglomerates well characterized by 

 fossiliferous pebbles of Devonian limestone, leaves no doubt 

 that in the main the " Clear Creek volcanics " near the Sacra- 

 mento are, as Hershey maintains, older than the Bragdon. 



On Backbone Creek, several miles above Kennet among the 

 stratified rocks which appears to belong to the Devonian, there 

 are definite beds of volcanic debris which indicate that an de- 

 sites and rhyolites, like those of the " Clear Creek volcanics," 

 were exposed to furnish Devonian sediments. The relation of 

 the Devonian limestone and shales in the Kennet region to the 

 " Clear Creek volcanics " confirms the same view. The Devo- 

 nian sediments appear in patches completely surrounded by the 

 " Clear Creek volcanics," at first suggesting that the Devonian 

 sediments are broken up and enclosed by the volcanics. On 

 closer examination, however, the isolated patches of Devonian 

 are clearly seen to be, for the most part, remnants of a once con- 

 tinuous but deformed sheet of Devonian that covered the " Clear 

 Creek volcanics " of that region, and was cut up by pre-Bragdon 

 erosion into separate patches exposing larger areas of the 

 underlying volcanics. A few miles northwest of Kennet the 

 Devonian patches lie on ridges completely separated by the 

 narrow canyon of Little Backbone Creek, but on Backbone 

 Creek erosion has not yet quite completed the separation of the 

 Devonian masses upon its sides. 



The " Clear Creek volcanics" of the Kennet area which are 

 beneath the Devonian, Mr. Hershey regards as on top of the 

 Devonian. If his view were correct, they should lie between 

 the Bragdon and the Devonian, which is certainly not true in 

 the Kennet region where all three are well exposed, and in 

 every Devonian outcrop touched by both Bragdon and u vol- 

 canics" the former is on top and the latter beneath. This 

 relation is clearly exposed at two points on Backbone Creek, 

 also on Little Sugar Loaf Creek, at the head of Bailey Creek, 



