Annual report of the State Mineralogist for the year ending ... . several miles in width, and containing broad river beds filled withgravel to very considerable depths. The rivers, in eroding the bedrockand forming these depressions, left a succession of broad, flat bencheswith shallow accumulations of gravel. The channels naturally followed, to a great extent, the belts of softslate. This slate is easily eroded, slacks readily, and is washed awayin the form of a fine silt. Quartz is the only important material con-tained in the belts which is hard and permanent enough to resist thedestructive

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Annual report of the State Mineralogist for the year ending ... . several miles in width, and containing broad river beds filled withgravel to very considerable depths. The rivers, in eroding the bedrockand forming these depressions, left a succession of broad, flat bencheswith shallow accumulations of gravel. The channels naturally followed, to a great extent, the belts of softslate. This slate is easily eroded, slacks readily, and is washed awayin the form of a fine silt. Quartz is the only important material con-tained in the belts which is hard and permanent enough to resist thedestructive action of the current. Owing to these facts we find in thefilling of the channel, for long stretches, quartz gravel and quartz sand *The term channel system herein refers to the beds of contemporary streams.2927 438 REPORT OP THE STATE MINERALOGIST. almost to the exclusion of other materials. The white channel of theMountain Gate and Hidden Treasure Mines is a striking example. (SeeFig. 3.) 4500 fig 3 4000 3500 HIDDEN TREASURE CHANNEL— CROSS-SECTION — 3000. IOOO«<°iWlule (Juain-ginuel^^=Vi]e-(jlay and Sand 2000- •yr.Blite tjnivt) 4000 5000 600C •AllVolcfinir qranel The channel is filled to a depth of fifty feet, and a width of one thirdof a mile, almost exclusively with smoothly washed bowlders, pebbles, and sand of pure white quartz. On top of this, to a depth of one hun-dred and fifty feet or more, and an original width probably exceeding amile, the filling is quartz sand and sandy pipe-clay. The course of these belts of soft slate being south, or somewhat eastof south, and not entirely continuous, and the general slope of the sur-face being to the southwest, the channels occasionally break across theharder belts of bedrock. The quartz gravel decreases in quantity, andthere are substituted pebbles and bowlders of equally hard siliceousmetamorphic rocks. There appears no conclusive evidence of the occurrence, during thisperiod, of any disturbances to cause a wide