ROCKS OF THE PRE-CRETACEOUS SERIES. 83 



Oregon line, and it is i)robable tliat rocks of the same age are to be found 

 in the Coast ranges of Oregon. Tlie existence of a pre-Cretaceous series 

 along the main crest of the Coast ranges in Tehama county has been 

 am})ly i)roved. A similar series is exposed in all those i)ortions of 

 Huml)oldt and Mendocino counties not covered by the Tertiary. As we 

 follow it southward it gradually becomes less prominent on the surface, 

 being covered to a great extent by the Cretaceous and Tertiary. The 

 farthest i)oint to which it can be traced southward is southern Santa 

 Barbara county, where it disapi)ears beneath the Cretaceous. For a 

 clearer idea of the distribution of these rocks in the Coast ranges the 

 reader is referred to a mai) published in the American Geologist for 

 February, 1893. It will be seen that south of Clear lake the exposed 

 areas diminish very materially. Numerous small areas, which are not 

 indicated on the map, are scattered through the Coast Range region, and 

 it would seem probable that, with the exception of the granitic axes, it 

 everywhere forms the basement on which the Cretaceous was laid down. 



No attempt will be made to define its boundaries in the Klamath 

 Mountain region, where rocks varying in age from the Jura-Trias to the 

 Devonian are known to exist; nor is it known in what relation the pre- 

 Cretaceous series of the central Coast ranges stands to the older rocks of 

 Trinity and Shasta counties, but it is believed that much of it represents 

 the last sediments deposited before the great upheaval terminating the 

 Jurassic. The metamorphism gradually increases toward the north, 

 where the rocks become fully crystalline. 



Lithology of the noncrystaUlne Portion of the Series — Jasper or Phthanite. — 

 The jaspers or phthanites, as they have been termed by Dr Becker, are 

 the most characteristic rocks of the series. They are widely distributed, 

 though tlieir total area bears a small proportion to the whole. They 

 form so striking a feature that they have been i)articularly referred to 

 by all the earlier geologists. The Ijeds consist of thin bands of silica, 

 which under the miscroscoi)e is shown to be a mixture of amorphous 

 and crystalHne silica in varying pro[)ortions, together witli iron oxides 

 and aluminous matter. Tin; l)ands range in thickness from lialf an inch 

 up to several inches, witli thin partings of argillaceous matter. As a 

 general thing the bands are more or less crumples and filled with iiiiiuite 

 interlacing quartz veins. 



Blake^' refers to these jaspers as much contorted and crumpled, ril)b()n- 

 like and filled with veinlets of white quartz. He sujii)Osed that they 

 had resulted from the metamorphism of sandstone and shale by igneous 

 action. 



• Pacific Railroad Survey, vol. v, p. 155, 



