T. Mellard Reads — Physiography of the Lower Trias. 157 



to which I answer, " Yes, plenty," but also add that such a size is not 

 common in the Bunter of Lancashire and Cheshire. 



According to the experiments of Mr. Blackwell, 1 made in a trough 

 of elm 60 feet long, 4 feet wide, and 3 feet deep, set horizontally, 

 a current of water having a velocity of from 105 to 125 feet per 

 minute, started a boulder weighing 11-87 ozs., and with a current of 

 from 165 to 180 feet it was carried along at the rate of 90 feet per 

 minute. These velocities, the lowest about a knot per hour, and the 

 highest rather less than two knots, are, as I have shown, frequently 

 exceeded by tidal currents, and the size of the boulder in question is 

 far above the mean of those of the Pebble Beds. 



Captain Beechy, who investigated the tides of the Irish Sea, says 

 of the tide entering the North Channel, " The main body sweeps to 

 south by east, taking mainly the general direction of the Channel, 

 but pressing more heavily on the Wigtonshire coast ; off which it 

 has scooped out a remarkable ditch upwards of 20 miles long by about 

 a mile only in width, in which the depth is from 400 to 600 feet greater 

 than the general level of the bottom about it." Again, between Glas 

 Island and Sqeir-i-Noe, in the Little Minch off the west coast of 

 Scotland, the flood- stream often takes the buoys of the long lines 

 down ; "and it is a remarkable circumstance indicative of the great 

 depth of the tidal stream here, that the buoys, though anchored in 

 70 or 80 fathoms, are taken completely to the bottom ; star-fish 

 and other marine animals being found attached to them." 2 These 

 instances might be multiplied, but there are evidences of strong 

 currents at much greater depths in the ocean; for instance, while 

 laying the Falmouth Cable near Gibraltar at 500 fathoms, "the wire 

 was ground like the edge of a razor, and we had to abandon it and 

 lay a cable well in shore." 3 These facts will be found fully detailed 

 in a paper on "Tidal Action as a Geological Cause" (Proceedings 

 of Liverpool Geol. Soc. 1873-4), and "Tidal Action as an Agent of 

 Geological Change," Phil. Mag. May, 1888. 4 



One of the characteristics of the pebbles of the Bunter is their 

 extreme smoothness and roundness, and I venture to suggest that 

 the rolling about by tidal action from day to day amongst siliceous 

 sand, together with the wash of sand over and against them, would 

 produce more efficacious polishing and give more travel than even 

 the longest river we may postulate. But it is not to be assumed 

 that all the pebbles were polished in deep water ; for if the beds are 

 marine in origin, littoral deposition and wave action are not excluded. 

 I think I have now answered the most material parts of Professor 

 Bonney's useful criticisms, and as I have no personal observations 

 to record on the Nagelflue and Molasse, to which he compares the 

 Bunter, I must refrain from any observations thereon. 



1 These were made for the Eeferees of the Metropolitan Drainage. 



2 Sailing Directions for the West Coast and Islands of Scotland, from the Mull of 

 Cautyre to Cape Wrath, p. 119. 



3 Extract from letter from Sir Jas. Anderson to the writer. 



4 See Mr. Arthur Hunt's letter on "Tidal Action," infra, p. 191. — Edit. 

 Geol. Mag. 



