The Quarterly journal of the Geological Society of London . Q. J. G. S. No. 185. 66 MR. H. J. MARTEN ON SOME weighed 16 lb. 12 oz., thus giving the weight of a cubic foot ofsaturated stone, as lying in the quarrj^ and in the apron of the weir,as 134 lb.; and the weight of each stone when placed in the weirwas estimated on this basis. The stones taken out of the weir werealso weighed in a saturated state. The pebbles were probably rolled by the current in flood-times upthe somewhat steep up-stream face of the weir, and deposited, aspreviously described, in the hollows and joints of the stones f
The Quarterly journal of the Geological Society of London . Q. J. G. S. No. 185. 66 MR. H. J. MARTEN ON SOME weighed 16 lb. 12 oz., thus giving the weight of a cubic foot ofsaturated stone, as lying in the quarrj^ and in the apron of the weir,as 134 lb.; and the weight of each stone when placed in the weirwas estimated on this basis. The stones taken out of the weir werealso weighed in a saturated state. The pebbles were probably rolled by the current in flood-times upthe somewhat steep up-stream face of the weir, and deposited, aspreviously described, in the hollows and joints of the stones formingthe flat apron or down-stream side of the weir (see figs. 7 & 8). Figs. 7 & 8.—Plan and Section of the Holt Weir on the « ! I I I Wllllltllim Scale Jor Weir When the weir was first constructed, the current on the up-streamface was so strong that boulders of considerable size were drivenover the crest. The average quantity of water passing over each square foot ofthe surface of the stones composing the apron of the weir is esti-mated at about 2000 gallons a minute ; each gallon of water has anaverage scrubbing-velocity of from 12 to 15 feet per second, and this,acting on the small pebbles, will give some idea of the forces atwork for the 43 years during which the stones were in the weirapron. There are not many instances in which the specific facts relatingto the action of water and pebbles upon a certain class of stone canbe so accurately ascertained as in the present case ; and the writerhas therefore ventured to submit a record of them, in the hope thatthey may be of use to those who may have occasion to investigatethe periods of time likely to be occupied in changes resulting fromthe abrading actio
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