114 WARREN DUPRE SMITH AND EARL L. PACKARD 



Table I, compiled by Mr. Fred Melzer, a Senior in the depart- 

 ment of Geology at Oregon in 191 7, gives at a glance most of the 

 general information about our igneous rocks, such as types, locali- 

 ties, frequency of mention in the literature, and the literature 

 citation. From a study of the literature we find that, judging 

 from the number of times mentioned in the literature, the various 

 types of basalt come first, andesites next, followed by metagabbro 

 third, and then comes rhyoHte with diabase and diorite a little 

 farther in the rear. 



The dominant rock in the Cascade region is the Columbia lava, 

 which is basaltic. The principal rock in the Cascade superstruc- 

 ture is andesite. In the metalliferous districts of the southwest and 

 northeast granodiorite is the chief rock. For a petrographic 

 description of this and the following rocks the reader is referred to 

 Table I. 



The serpentinized peridotites in the vicinity of Port Orford are 

 both interesting and valuable economically because of the associa- 

 tion of chromite and nickel. According to Diller they were prob- 

 ably intruded in Cretaceous times. 



It will be seen from the testimony of the literature that the 

 dominant igneous activity in the state has occurred later in geologic 

 time, in the Mesozoic and Cenozoic. Very little is definitely known 

 of the igneous rocks of the Paleozoic, and little or nothing of the 

 pre-Cambrian, if indeed there were any at all at that time in this 

 state. 



Chemically the rocks are alkali-calcic. According to Iddings,^ 

 "the 76 igneous rocks of the Cascade Mountains that have been 

 analyzed belong in 24 magmatic divisions of the Quantitative sys- 

 tem, 56 falling in 5 divisions: tonolose 22, lassenose 11, andose 9, 

 hessose 8, and yellowstones 6, all of which are dosodic. Only 9 

 of the 76 analyzed are sodipotassic." 



Steinmann^ asserts that the average igneous rock of the South 

 American Cordillera is similar to that of the Pacific Coast of North 

 America. He says that the lavas of the former region are ande- 

 sites, dacites, and rhyoHtes, and that granodiorites are the pre- 



' J. P. Iddings, Igneous Rocks, II, 446. 



^ G. Steinmann, Geolo. Rundschau, I (1910), 13. 



