LOWER CRETACEOUS. 617 



at least two unconformities separating tlie Eaioxville-Cliico beds into important stratigraphic 

 groups will be made out on further study. * * * 



A zone of coarse conglomerate varying in thickness from less than 100 to over 1,000 feet 

 extends intermittently from the summit of Juniper Ridge, south of Los Gatos Creek, to a point 

 south of Reef Ridge, in Big Tar Canyon. It is overlain and underlain, in appearance conform- 

 ably, by the thin-bedded dark shale and bandstone of the lower half of the Kjioxville-Chico. 

 The portion of the terrane lying below this conglomerate is here classed by itseK as the lower 

 division. * * * The total thickness of the lower division as exposed in the Alcalde Canyon 

 section is between 3,100 and 3,500 feet. * * * 



Fossils of Knoxville (Lower Cretaceous) age, such as AuceUa crassicoUis Keyserling and 

 Belemnites impressus Gabb, have been found in beds of dark shale in the Devils Den region 

 not many miles south of the Coalinga district, and there is httle doubt that the lower division 

 of the rocks here described as Knoxville-Chico is at least in part the equivalent of the Knoxville 

 formation. It is possible that the great beds of conglomerate mark the base of the Chico 

 or Upper Cretaceous and that the whole of the lower division below this line of separation 

 represents the Knoxville formation. 



For reference to the views of F. H. Knowlton and James Perrin Smith on the 

 Jurassic age of that part of the KJioxville which contains a Jurassic flora, see the 

 next section (K 10). 



For a general correlation table of the Mesozoic and Cenozoic formations of 

 the Coast Range, see Chapter XVII (p. 818). 



K 10. KLAMATH MOUNTAINS, OREGON AND CALIFORNIA. 



In his published articles Diller ^''^ has recognized representatives of the Knox- 

 ville, Horsetown, and Chico of the Cahfornia Cretaceous section in the Klamath 

 Mountain section. 



The strata of conglomerate, sandstone and shale, which are believed to represent 

 these epochs, are comprised in the Myrtle formation. The strata are irregular, 

 but shale predominates. The coarser detritus is derived from disintegrated granite. 

 In the Roseburg quadrangle the thickness is estimated at about 6,000 feet. Fossils 

 from the upper portion include Pecten operculiformis and Trigonia cequicostata, 

 characteristic of the Horsetown epoch. Aucella crassicoUis and A. piochii are found 

 in the lower portion, the equivalent of the KnoxviUe. The Myrtle formation 

 includes limestone lentils which contain Opis calif ornica and Hoplites dilleri or a 

 form closely related to it. These are also found in the Knoxville. 



The Myrtle formation is bounded by very marked unconformities both above 

 and below and is intruded by igneous rocks and metamorphosed.^'^^' ^" 



The relations of the Myrtle formation to the Horsetown and the upper part 

 of the Knoxville are apparently established beyond doubt by the common occur- 

 rence of Aucella piochii and A. crassicoUis in similar stratigraphic relations in both 

 areas, as well as by the abundant floras which have been found in both formations 

 and which are intimately associated in Oregon with both species of Aucella. It 

 is not clear, however, that the Myrtle formation includes older strata that should 

 correspond to the middle and lower parts of the Knoxville. The KnoxviUe is 20,000 

 feet thick. The Myrtle, so far as known, is but 6,000 feet thick. Diller regards this 

 known portion of the formation, which rests on a basal unconformity, as the thin 



