Hebshky.] The River Terraces of the Orleans Basin. 



probable from the slope of the surface, and the great predomi- 

 nance of slate pebbles and boulders. (Camp Creek drains a slate 

 country). No means were at hand for accurately determining' 

 the altitude of Owl Flat, but from various points of view it 

 seems to be slightly higher than the Donahue Upper Flat, 

 although the bed-rock floor of the two channel remnants is prob- 

 ably of similar altitude. By considering it a deposit largely of 

 Camp Creek, it may be referred to the same stage as the 850-foot 

 terrace without any difficulty being raised by the great thick- 

 ness of the deposit and its superior height. Small patches of 

 gravel are known to exist at about the level of the Owl mine, 

 along the north side of the Lower Basin, for a mile and a half 

 downstream.* 



The 675-Foot Terrace. — This is represented by a single rem- 

 nant, but it is so extensive as to be the finest development of the 

 upper terraces. It lies north of Orleans and has an east-west 

 course. The surface is cut into two flats by a deep ravine. The 

 most easterly, Bacon Flat, has an extent of twenty-seven and 

 one-half acres. Its average altitude is 1,150 feet. For such an 

 old terrace, the surface is remarkably even. A ditch on the river 

 side displays the following section in descending order : 



BACON FLAT SECTION. 



Thickness 



1. Deep red, horizontally but indistinctly stratified 



clay, containing small, angular fragments of 

 Bragdon slate and quartz 17 feet. 



2. Light brown clay, containing much tine river 



gravel 3 feet. 



3. Light reddish brown stiff, sandy clay, containing 



a few small river pebbles o feet. 



4. Light reddish brown argillaceous sand, contain- 



ing some small river pebbles 5 feet. 



5. Light brown rather fine river gravel, no cobble 



exceeding six inches in diameter, most under 

 four inches and many only one inch in diam- 

 eter 40 feet. 



Total 70 feet. 



Base of gravel not seen. 



*The Owl Mine building is situated on a small flat eighty-five feet 

 above bed-rock in the mine, and forming the floor of a small amphitheater. 

 Two-thirds of the distance to the top of the steep slope forming the 

 wall of the amphitheatre there is a fresh perpendicular scarp (due 

 to sliding of the gravel toward the mine) five to ten feet high. 

 At the time of my visit, March 18, 1904, the length of this scarp had 

 been increased several inches all along the wall since the last rain, on 

 the morning of the preceding day. 



