S. WASH] IE SALTS ND PLATEAU BASAL 



On the one hand, these norms st lo the analyses, the greater 



variation among the Oregonian as compared with the Deecan basalts, 

 rlv half of them contain olivine and no quartz, and the quartz con- 

 tent of the Teanaway and Yakima basalts is higher than in any of the 

 Indian ones. On the other hand, we see here mnch the same general 

 characteristic featur— - ire did in the previous series. There is the 

 same general equality in the amonnts of albite and anorthite. with albite 

 relatively higher in the more silicic rocks, as is also orthoclase. Diopside 

 and hypersthene are again approximately equal, but here there is not the 

 general increase in hypersthene as compared with diopside that was 

 noted before. The augite here also is evidently an enstatite-augii-. 



Thuxeax Basalts 

 :-i eral d1bcu88ios 



We now take up for consideration a third great area of plateau basalts, 

 which were poured out (for the most part probably during the ne) 



over the large landmass that once occupied much of the present north 

 Atlantic and of which only a few small and disconnected fragments 

 survive. 16 



Fragments of this extensive basaltic area are found in northern Ire- 

 land, western Scotland, east renland (and possibly in west Greenland ) . 

 and the islands of the Hebrides, Shetlands. Orkneys. Faroes. Iceland, 

 Jan Mayen. Spitsbergen, and Franz -Josef Land. The essential simi- 

 larity and presumably common origin and relationship of these basalt 

 flows have been generally recognized by those who have written on the 

 region. I have been able to study specimens from only Iceland and the 

 Faroe Islands, but the basalts of other parts will be described briefly. - 

 - I give a general idea of the whole region. 



The name "TSrito- Arctic" has been applied to this region by British 

 petrologists. but this appellation is open to the objection that only small 

 parts of Great Britain and of the Arctic are included in it. The name 



Ulean." proposed here for this region of plateau basalts, is derived 



from the name Thule, given by Pytheas toward the end of the fourth 



century B. C. to a somewhat vague and as yet undefined and not wholly 



identified island or region lying to the north of the British Islands. It 



as advisable thus to distinguish the basaltic plateau from the De- 



34 The literature on this region and its rocks is so abundant and varied that only a 

 few references, of a more general character, need be cited. Geikie: Ancient volcanoes 

 of Great Britain. toL ii. 1S97. pf 181-297 ; Textbook of Geology, toL L p. - " .. ii. 



1903. p. 1252: Harker : Natural history of igneous rocks. 1909. pp. 19 and 99: S: 

 The face of the earth (English translation i , toL It, 1909, pp. 258-2 1 Holmes and 

 Harwood : Min. Mag.. roL 18, 1918, p. I 



