M I'RRIAM.] 



John Day Basin. 



305 



deposit about two feet thick, caught in the midst of the dike, show 

 a diameter of about five inches. Evidently the greater heat and 

 slower cooling tended to increase the size of the columns. 



As far east as the writer's observations extend, viz., to Dale on 

 the north and Mt. Vernon on the south, the Columbia lava has 

 formerly covered the whole country. There do not appear to 

 have been any islands in this sea of stone. Over most of this 

 region the lava beds still remain fairly flat. They are rarely 

 inclined more than five or ten degrees. 



Along the north side of the East Eork Valley from Mt. 

 Vernon to Picture Gorge, and from there westerly toward 

 Caleb, the Columbia lavas are inclined sharply to the south. 

 Along the valley they pass beneath the river and below the 

 Mascall formation. At Picture Gorge, where the lavas are cut 

 through by the river, they show a dip of about twenty degrees or 

 more to the south. On the south side of this valley the southern 

 range of the Blue Mountains is capped with Columbia lava. In 

 the Crooked River region the lavas appear again beneath the 

 Mascall formation. 



Viewing the East Fork Valley from near Caleb it is quite 

 evident that the Columbia lavas are sharply faulted or bent along 

 its south side, the downthrow being to the north. Near the west- 

 ern end of the valley a number of nearly vertical beds are exposed 

 high up on the southern slope. Persons who have visited these 

 outcrops inform me that they are lava, and I have supposed them 

 to be beds dragged down along the plane of a fault or sharp fold. 

 In the depression to the north of the fault plane there rest several 

 post-Columbia lava formations which, as will be shown later, have 

 also been affected by this disturbance. 



MASCALL FORMATION. 



Nomenclature. — Along the valley of the East Fork and south of 

 the Blue Mountains, there is found, resting upon the Columbia 

 lava, a series of sediments which have been known in the literature 

 as the Cottonwood* beds, the Loup Forkt beds, the TicholeptusJ 



*Bull. Am. Mus. Nat. Hist., Vol. XII, p. 23, also Jour. Geol., V. IX, p. 72. 

 t Manual of Geology, 4th Ed., J. D.Dana., p. 895. 

 + E. D. Cope, Am. Nat., 1886, V. 20, p. 367. 



