828 INDEX TO THE STKATIGRAPHY OF NORTH AMERICA. 



exposed as steep, pinnacled, and ribbed bluffs. Nodular layers and thick beds with small 

 nodules scattered through them are common in this group, whUe they are rare, if not entirely 

 absent, in the lower division and are not common in the uppermost beds. The strata of this 

 group are never so sharply contorted as those of the lower division, though they may stand at 

 a fairly high angle and may show considerable faulting. 



This stage has probably furnished more fossil remains than the upper division, partly 

 because the remains are here frequently found in hard nodules, which have protected the bones 

 and held them together. 



At Bridge Creek a rhyolite flow is interbedded with the lower part of the Middle John Day 

 or possibly separates it from the lower division. In Turtle Cove a similar flow is found at the 

 top of this division and possibly separates it from the upper group. At many places, particu- 

 larly in Turtle Cove, hard beds -of white to greenish ash and tuff are intercalated between the 

 softer and usually more fossiliferous strata. 



The middle division is at least 500 feet thick in Turtle Cove and possibly as much as 800 

 to 1,000 feet at Bridge Creek. 



At most John Day localities, including Bridge Creek, Turtle Cove, and the entire region of 

 the North Fork, the uppermost beds in the section are buff tuffaceous or ashy deposits, some- 

 times with sand and gravels near the top. These beds show a thickness of at least 300 to 400 

 feet and perhaps much more in some localities. 



***** **** 



This division contains the only typical sands and gravels in the John Day, and the only 

 known remains of fresh-water MoUusca occur here. Excepting a single leaf, the only plant 

 remains known to occur in the series are in the upper division. 



WhUe it has not been possible for the writer to draw sharp lines between the divisions 

 discussed, the lithologic characters are in general sufficiently well marked so that one is enabled 

 to determine the horizon in the series to which beds in question belong. 



The John Day beds are usually slightly disturbed. They are generally tilted 5° to 10°. 

 From the observations made by the writer, no definite system of folds could be made out, 

 though there seem to be several which trend east and west. Faulting is not uncommon and 

 in some places there has been much friction along the fault planes, so that the soft beds have 

 been changed into hard slate bands several inches in thickness. Both the normal and reverse 

 types of faults are represented. Toward the west end of Haystack Valley a break of unknown 

 extent brings what are probably Middle John Day strata up to the level of the highest beds of 

 the series. At another locality, some miles east of this point, numerous thrusts are beautifuUy 

 shown in cliff sections. Along the North Fork two systems of fractures were noticed. One 

 trends north and south and the other appears to cross it at nearly a right angle. 



As has already been indicated, the series is evidently unconformable upon the Clarno. 



In the whole of the region occupied by John Day north of the southern range of the Blue 

 Mountains, it is covered by the Columbian lavas, being accessible only in the deep canyons, 

 where it has been exposed by extensive stream corrasion. At every locality in the basin where 

 the series can be seen, its relations to the overlying formations are beautifully shown. In 

 several places, notably at Sheep Rock in the upper end of Turtle Cove, and on the main river 

 below Spray, residual hills in the middle of the valley are capped by portions of the lower flows, 

 which have served to protect the softer beds beneath. 



The Columbia lavas are in some places seen to be decidedly nonconformable to the John 

 Day. Near Haystack the fossil beds form a fairly sharp anticline below lavas which are almost 

 horizontal. At Clarno's Ferry lava flows are seen at one locality to rest upon the middle beds, 

 the typical upper divisions being absent. 



