hershky.] The River Terraces of the Orleans Basin. 



433 



exposed in mining is about seventy feet in average height. It 

 exposes three principal types of deposits, but the thickness of 

 each varies greatly from section to section. At the base there 

 is moderately fine river gravel from five to thirty-four feet 

 thick, but mostly ten or fifteen feet thick. Until recently a 

 boulder requiring blasting was rarely encountered, but now the 

 operations are uncovering a bed of large, waterworn granite 

 boulders, apparently of a local origin. Over the gravel there is 

 usually light reddish brown and gray non-pebbly sandy silt, one 

 to twenty feet in thickness. ^ The remainder of the bank dis- 

 plays an irregularly stratified but perfectly waterworn mixture 

 of fine gravel, sand and clay, in which local slate debris, prob- 

 ably from Sims Gulch, plays an important part. Near the 

 surface this deposit is largely replaced by nearly non-pebbly 

 clay. The color is a bright brick red, varying to reddish brown. 

 The deep red stain extends down fifty feet or more ; in fact, to 

 the gravel bed and deep into the latter where there is sufficient 

 iron oxide. Blue gravel is not found except in one shallow bed 

 near bed-rock. In other words, the deposit is thoroughly oxi- 

 dized nearly to the base, even at the center of the original flat. 



Directly opposite Sims Gulch there is another remnant of 

 this same terrace, apparently as extensive as the original Brown 

 Flat. Sims Creek has cut a sharp canon several hundred feet 

 across this terrace. 



The residual above mentioned is a narrow, uneven-crested 

 ridge, about half a mile long, and reaching a maximum altitude 

 of 1,113 feet, or 638 feet above the river at Orleans. No traces 

 of the Brown Flat deposits are found in the deep, narrow Camp 

 Creek Valley on the west side of the residual, but Kentucky 

 Flat, at the extreme southern end and just above the old Graham 

 Flat mine, is evidently another remnant of the same terrace. 

 It has an average altitude of 943 feet and an extent of probably 

 five acres. 



The 120-Foot Terrace— Tine Rocky Point Mine is situated 

 on a point on the south side of the river, near the upper end of 

 the Upper Basin. It has a waterworn but irregular rock bench 

 of black slate at a level approximately eighty feet above the river. 

 This is covered by five to fifteen feet of very coarse river 



