MESOZOIC OF SOUTHWESTERN OREGON 555 



Coast Range region of California was largely under water, at least 

 so far south as about latitude 34° 30' N. This sea invaded the 

 Oregon coast at least as far north as latitude 43 15' N. 



Following the deposition of these beds — perhaps in part during 

 it — at least three series of igneous rocks were intruded at separate 

 intervals; a basic series (basalts, diabases, etc.); an ultrabasic series 

 (serpentines, pyroxenites, gabbros) ; and an acid sodic series (dacites, 

 andesites). There is also evidence of elevation of the Franciscan 

 sediments to dry land, dislocation, fracturing, crushing, considerable 

 cementation and veination, and, finally, a long period of erosion, 

 which stripped the sediments from the granular intrusives over large 

 areas. This whole course of events, of sedimentation, vulcanism, 

 cementation, diastrophism, and erosion, follows closely, in sequence, 

 characters, and intensity, the history of the corresponding time 

 throughout the California Coast Range province, and extends the 

 recognized limits of this province almost 100 miles, making the 

 extreme length now known about 600 miles. 



Following the period of erosion came another period of dominating 

 subsidence, and the gradually transgressing sea, which deposited 

 chiefly fine sediments with some sand and well-washed gravels, 

 built up the upper (Myrtle) group of rocks, which reach the thickness 

 of about 6,ooo feet near Myrtle Creek. These are more or less fos- 

 siliferous and contemporaneous — probably continuous — with the 

 Shasta group of California. The sea entered this Oregon region 

 apparently as an arm elongated in an east-west direction, with its 

 south shore against the Klamath Mountains and its north shore 

 about the latitude of Roseburg. The land to the north showed 

 chiefly Franciscan exposures ; that to the south, both Franciscan and 

 the earlier crystalline schists, etc. With the progress of Shasta time 

 this arm broadened, and finally united with the gulf which was 

 advancing over northern California around the other side of the 

 Klamath Mountains, making of this mountain group an island, which 

 may possibly have been finally submerged. 



The glaucophane and associated schists of southern Oregon were 

 formed during the same period as the similar schists in California 

 (pre-Knoxville) and are associated with similar rocks of the same 

 (Franciscan) series. 



