1858.] ORMEEOD EOCK-BASINS. 21 



On this, there are several long, oval, concave, shallow hollows, point- 

 ing up and down stream ; the sweep of the water carries the stones 

 along and over these, the grinding action adding apparently to the 

 length in a far greater degree than the breadth. The measures of 

 six hollows at this place are 7 inches by 16 in diameter, and 3 

 inches deep ; 8 inches by 12 in diameter, and 1 inch deep ; 9 inches 

 by 14 in diameter, and 1 inch deep ; 9 inches by 18 in diameter, 

 and 4 inches deep ; 10 inches by 12 in diameter, and 2 inches deep ; 

 12 inches by 27 in diameter, and 3 inches deep. The river in floods, 

 after passing over this rock, falls nearly perpendicularly about 6 feet 

 into some '^ pot-holes." One of these nearly circular is 23 inches by 

 24 in diameter, and 15 inches in depth, and at the bottom there 

 are large round stones ; the sides are nearly upright, curving in at 

 the bottom, which appears to be concave ; but, in consequence of the 

 quantity of water at the time when the examination was made, this 

 point was not clear. Another is 12 inches by 10 in diameter, and 

 more than 26 inches in depth. This '• pot-hole " enlarges a few inches 

 above the bottom, having probably penetrated a softer bed of granite, 

 and the lower part is nearly filled with round stones ; for the same 

 reason as above mentioned the bottom could not be examined. In 

 both these cases the direct downward action of the stream would 

 give very considerable motion to the stones. On the adjoining but 

 more open rock on this lower level, exposed to the horizontal sweep 

 of the flood, but not so directly as at the top of the rapid, the hoUows 

 are again of the long oval shape, but the longitudinal section is dif- 

 ferent. The rush of the water not being here so violent as above, 

 stones remain at the upper ends of the hollows, being there protected 

 against the current ; and, there rotating, wear deep holes, which on 

 the side up stream are nearly perpendicular, and on the opposite 

 side slope gradually away to the lower end of the hollow. If the 

 *^ basins " are compared with these " pot-holes," we flnd the majority 

 to be here concave and irregular ; there to have the bottoms flat and 

 regular with upright sides ; here in those having upright sides the 

 depth is excessive in proportion to the diameter, there it is the 

 contrary. 



Sir Henry De la Beche, in a note on the ' Eeport on Cornwall, 

 Devon, and West Somerset' (p. 452), writes : — " Dr. M'Culloch has 

 suggested that the friction of the quartz and felspar fragments not 

 unfrequently found in rock-basins may have contributed to deepen 

 them. As we have often observed these fragments in motion during 

 high winds, both when the basins were dry, or a small quantity of 

 water in them, we are inclined to beheve that this may be the case." 

 These fragments occur in most basins ; in some, as shown in the table, 

 the bottom is covered by them. Rolled stones similar to those which 

 occur in the " pot-holes " have not been foimd by the Author in any 

 basin, but the contents generally consist of a small angular fragment 

 of quartz and felspar, as above mentioned, and schorl, which some- 

 times, as shown in the following table, cover the bottom of the basin. 

 Small lumps of granite occasionally are found not rolled, but that 

 have apparently fallen in where the sides are much weathered and 



