MESOZOIC OF SOUTHWESTERN OREGON 525 



THE UPPER GROUP 



General composition. — In lithologic characters the upper group 

 differs considerably from the lower. The most abundant and 

 characteristic rock type is shale, then sandstones and conglomerates. 

 No trace of radiolarian cherts or cherts of any type, occurs in this 

 group, nor do foraminiferal limestones corresponding in general 

 character to the Whitsett lenses, although there are calcareous shales. 

 The most striking general difference between the lower and 

 upper divisions is the markedly inferior lithification of the latter. 

 Although it has been compressed into large folds, and to some extent 

 faulted, and even locally crushed, especially where it has been thrust 

 against the more massive older rocks in the course of its folding, 

 yet, in general, its lithologic characters have been comparatively 

 little altered. 



Shales. — The shales, which are the predominating rock type, are 

 characteristically of a greenish-gray color, sometimes pure gray, and 

 their stratification and lamination, except occasionally where locally 

 crushed, are always readily discernible, and the dip and strike meas 

 urable, and the beds and structures may be traced for considerable 

 distances without great effort. No slaty structures are developed, 

 and hardened facies are rare. A spheroidal structure is not uncom- 

 mon, but the original lamination is always distinct. Moist samples 

 of these shales smell strongly of clay. 



The shales are commonly more or less calcareous, and some are 

 highly so and may be called argillaceous limestones. 



Sandstones. — Interbedded with these shales are rather thin- 

 bedded sandstones from two or three inches up to not generally over 

 several feet thick, though occasionally heavier beds occur. They 

 are commonly brown, sometimes buff or greenish, and never show 

 the peculiar gray compact facies so often seen in the sandstones of 

 the lower series. In some parts of the series the shales greatly pre- 

 ponderate over the sandstones; in others they may be in about 

 equal quantity, or occasionally the sandstones may actually prevail. 

 On account of their general thin-bedded character and the regularity 

 of the bedding, the attitude of these sandstones can generally be 

 readily determined and measured. 



The material of which the sandstones are composed is, as in the 



