316 University of California Publications in Geology [Vol. ll 



In addition to these basalts, the cherts are associated with diabase 

 and gabbro, and in the southern Kenai Peninsula dunite occurs with 

 the cherts. Besides the basic igneous rocks, the cherts are cut by 

 dykes of dacite porphyry. 



Palache makes the following statements concerning these rocks : 



With the exception of the dike rocks, this section bears an altogether extra- 

 ordinary similarity in structure and lithologic character to the radiolarian cherts 

 and associated igneous and clastic rocks of the Franciscan Series of the Cali- 

 fornia Coast Range, especially well developed on the San Francisco Peninsula. 



In addition to the rocks above described, there are slates, gray- 

 wackes, cherts, and greenstones in this region which are considerably 

 more deformed and broken and show more metamorphism than those 

 referred to the Upper Triassic. These are associated in some places 

 with glaucophane schists. The exact relations of this group are un- 

 certain. They may be an older series or may be the metamorphosed 

 equivalents of the Upper Triassic cherts. 



CODDEN HILL BEDS 



Bedded radiolarian cherts occur in the Culm of southwestern 

 England in Devon, Cornwall and West Somerset. The radiolarian 

 cherts of this area have been called the Codden Hill Beds. 59 The 

 Culm measures consist of a basal series of dark argillaceous shales 

 containing persistent beds of dark limestones. Above these come the 

 radiolarian cherts with their interbedded shales, and overlying them 

 is a series of sandstones, grits, and shales. 



The cherts occur in beds that as a rule range in thickness between 

 two and four inches. Some are only an inch thick, while others may 

 be as much as nine inches thick. The color varies somewhat, ranging 

 from white to light gray, bluish, dark gray, to black. They are 

 crossed by many joint planes perpendicular to the bedding surfaces, 

 which cause the rocks to break up into numerous small rhomboidal 

 blocks. They are often cut by veins of white quartz. 



Alternating with the beds of chert, are shaly beds, usually of a 

 white or grayish color. They are much thinner than the cherts, in no 

 case exceeding two inches, and are sometimes lacking altogether. The 

 material of these soft shaly partings breaks up readily into thin 

 flakes or laminae when placed in water, and the softer varieties break 

 down into a very fine mud when so treated. 



59 Hinde and Fox, On a well marked Horizon of Eadiolarian Eocks in the Lower 

 Culm Measures of Devon, Cornwall and West Somerset, Quar. Jour. Geol. Surv., 

 vol. 51, p. 609, 1895. 



