MESOZOIC OF SOUTHWESTERN OREGON 523 



the constituents, and occasionally an actual schist has been locally 

 produced. 



Besides the development of a silicious cement, much of the sand- 

 stone is intersected by small and irregular quartz veinlets. These 

 are sometimes quite abundant, and occasionally larger veins some 

 inches across, or irregular bunches of quartz, are developed. Sec- 

 ondary calcite in small veins or irregular grains, etc., is also found. 



Some of the more silicified sandstone stands out in hard and 

 rather fresh exposures, while other parts weather down, assuming 

 a brownish color. Its general massiveness, folded and crushed 

 condition, and other properties make the determination of structural 

 features and measurements of sections exceedingly difficult. Occa- 

 sionally thin and distinctly bedded sandstones are found which may 

 be considerably less altered than those above described. They are 

 not characteristic, and are generally not traceable any great distance. 



The shales. — Shale occurs in subordinate amount associated with 

 the sandstone. It varies in color, being usually a rather pure gray, 

 more rarely greenish-gray, and is generally much crumpled, crushed, 

 broken, and slickensided, although exposures of less disturbed material 

 do occur. Occasionally it takes on a hard, slate-like habit and shows 

 distinct cleavage planes; again, it is so crushed as to show no planes 

 at all. Some parts show irregular secondary silicification, while 

 others seem very slightly altered. 



Conglomerates. — Conglomerate lenses are met at a number of 

 places and at apparently different horizons, but they can rarely be 

 traced very far and seem to be of little value in subdividing the series 

 into groups. They are frequently of jasper, quartz, and some other 

 pebbles. These pebbles are generally firmly cemented, so much so 

 occasionally that a fragment broken off by a hammer will show a 

 rather even fracture face passing through both pebbles and matrix, 

 the pebbles neither protruding nor breaking out, and leaving rounded 

 depressions. Faulted pebbles are quite common. 



Cherts. — Lenses and irregular masses of radiolarian chert are very 

 characteristic of the lower series. Along the coast quadrangles they 

 may be more abundant than the conglomerates, but in the Roseburg 

 quadrangle they are apparently less so. On account of their hard 

 silicious character, bright colors, and great resistance to weathering, 



