KNUWI.TON.1 GEOLOGICAL FEATURES. 19 



('OLLM15IA RIVER LAVA. 



So far a.s ran now hv made out the g;reat Coliinil)ia River lava once 

 covered practically the entire John Day country-, with few, if any, 

 points projectin(4al)ove it. Itconsistsof alarj^enuniber of l)asaltflows 

 which are sonietinies separated by beds of tuff, and it is estimated by 

 Dr. Merrian) to l)e not less than 1,000 feet in thickness, and in many 

 cases it seems to be still tliick(n'. 'Phis luva sheet has been compara- 

 tively little disturbed, remaiciing- practically tiat over the entii-e region, 

 l)eing rarely inclined more than 5'^ or 10°. 



MASCALL FORIVIATION. 



At several points within the basin there is a series of sediments 

 resting upon the Columbia River lava to which Dr. Merriam has given 

 the num(> Mascall formation. This series, or portions of it, has l)een 

 variously known in literature as the Cottonwood beds, Loup Fork 

 beds, llu' Ticholeptus IxkIs, the Amyzon Ix'ds in part, and finally the 

 Pr()t«)lal)is beds. For one reason or another these various terms are 

 ina})|)lical)le. Thus *■* Cottonwood" is preoccupied by its use for a 

 Carltoniferous formation in Kansas; its correlation Avith the Lou[) 

 Fork, the Amyzon beds, and the Ticholeptus beds is open to doubt, 

 lea\ing only W'ortman's term, Protolabis beds, which, in Dr. Merri- 

 aiu's opinion, will cover onl}^ a portion of the section. The name Mas- 

 call formation was suggested by the occurrence of the tvpical section 

 near the Mascall ranch, 4 miles below Da3'ville. 



At Kattk'snake Creek, near Cottonwood, the :\Iaseall is not less than HOO to 1,000 

 feet thick. The beds are made up larjjely of asli and tuff, and are generally h^dit 

 colored, thougli there are some l)ro\vnish and reddish strata. Coarse, detrital mate- 

 rials are generally absent from tlie typical section.^' 



The ]\Iascall formation has afforded a large and varied fauna, con- 

 sisting of manmials, testudinates, and ffsh, and a larg'e and interesting- 

 flora. The Van Horn's or Belshaw's ranch locality is in this forma- 

 tion, occurring near the ])ase of the section. The plants are preserved 

 in a soft, white, ffne-grained ash or tuff', which is often 1(> feet in thick- 

 ness, though usually less. This material is so light when dry that it 

 readily floats for some time on water. 



RATTLESNAKE FORMATION. 



Dr. Merriam has given the name Rattlesnake formation to a series 

 of coarse gi'avels, tufls, and rh^'olite flow^s that rest unconformablj- 

 u})on the Mascall formation. These beds are very slightly inclined, 

 showing a dip of only about 5^. 



a Merriam, op. cit., p. S07. 



