722 ABSTRACTS OF PAPERS 



aggradation of the Allegheny caused every tributary, including the Monon- 

 gahela, to aggrade, and the coarseness, limited upstream extent, slope, and 

 other characters of the tributary deposits indicate that those streams built up 

 as rapidly as the overloaded master stream. As each stream bed rose, it 

 reached the height of one after another of the low places in divides between 

 small tributaries, and at such times and places the currents of the rivers were 

 divided and the cols occupied. When final readjustment began, the rivers 

 chose the channels momentarily most desirable, and thus many parts of val- 

 leys were abandoned. The network of abandoned valleys near Pittsburgh is 

 looked on as a result of the processes above outlined. Some of the courses 

 are broad and were used for a long time, and others were only temporarily 

 occupied. It will be seen that the time represented by the abandoned valleys 

 and their deposits is far longer than that represented by the inner gorges. 

 The high terrace deposits are looked upon as probably Kansan in age, but the 

 processes of abandoning and partially filling the valleys lasted long enough 

 for at least two well developed valleys, such as we find here and at Belle 

 Vernon, to have been developed side by side. These old valleys are consider- 

 ably broader than the inner gorges through which the rivers flow today; 

 hence we must conclude either that Kansan time was much longer than all 

 the time that has elapsed since, or else — the more likely inference — that the 

 development and partial filling of valleys now abandoned progressed not only 

 through Kansan time, but other epochs. 



CRETACEOUS AND TERTIARY FORMATIONS OF WESTERN NORTH DAKOTA 

 AND EASTERN MONTANA 



BY A. G. LEONARD 



(Abstract) 



The formations occurring in the region under discussion are the Pierre 

 shales. Fox Hills sandstone, Lance formation (Ceratops beds), Fort Union, 

 and Oligocene. The Pierre and Fox Hills, which are marine formations, are 

 found along the Missouri River and its tributaries. The Lance formation 

 covers a large area in south-central North Dakota, where it has a thickness of 

 600 to 700 feet, and occurs also on the Little Missouri, Yellowstone, and Mis- 

 souri rivers. It is composed of shales and sandstones, the upper hundred feet 

 being a massive, yellow sandstone. Overlying the Lance formation is the Fort 

 Union, which contains most of the coal of the region. It is readily distin- 

 guished from the Lance formation by its light yellow and ash gray color, 

 as well as by its fossils. The Oligocene beds are restricted to a few small 

 areas in North Dakota and southeastern Montana. 



EOCENE AND OLIGOCENE OF THE WIND RIVER AND BIG HORN BASINS 

 BY WILLIAM J. SINCLAIR AND WALTER GRANGER 



(Abstract) 



Conformable superposition of Wind River on Wasatch and unconformable 

 Lower Oligocene on Uinta-Bridger-Lower Eocene have recently been found in 

 the Big Horn and Wind River basins, respectively, in northwestern Wyoming. 



