T. Mellard Reach— On the Lower Trias. 261 



significance of the examples of tidal action which I gave in my last 

 paper. 1 The quotation there given respecting the "remarkable 

 ditch " scooped out by the tide opposite Wigtonshire is in Captain 

 Beechey's own words. That very efficient and scientific officer had 

 no theory to uphold ; but the cause and effect were so clear to him 

 that he speaks without hesitation. I had marked years ago (1873) 

 on a large Admiralty Chart the stream tide lines taken from Captain 

 Beechey's survey, and this " remarkable ditch " is in exact parallelism 

 to them. There is also another striking example of excavation by 

 the tide at the northern entrance to the Irish Sea confirmatory of 

 this view. Opposite and north of Bathlin Island there is a " deep " 

 in which the greatest sounding is 133 fathoms = 798 feet, the sur- 

 rounding sea-bottom being from 60 to 80 fathoms only. A portion 

 of the bottom of this depression at a depth of 105 fathoms or 

 630 feet is rock, while the surrounding soundings in the shallower 

 water are sand and shells, a clear proof that the " deep " has been 

 excavated. 



Hurd " deep " opposite the "Casquets" in the English Channel 

 is another example of a long narrow channel where at a depth of 

 73 fathoms the bottom is rock, and at 95 fathoms sand and stones, 

 the surrounding bottom being from 30 to 40 fathoms only. The 

 form of the bottom of the sea below the depth at which wind waves 

 act is the resultant of the rub of the tide on the botto m at one place 

 and deposition of the eroded material at another. 



According to a letter received by me from Sir G. B. Airy, the 

 Astronomer Royal in 1873, the difference between the surface and 

 bottom velocities is the measure of the loork done by the tide on the 

 bottom. 



I think I may be excused repeating these facts and principles, as 

 I regret to say that the subject has hitherto received little attention 

 from geologists. 



Mr. Arthur R. Hunt (Geol. Mag. April, 1890, pp. 191-2) goes so 

 far as to assert that the tides in the English Channel, taking it as 

 a test case, have no effect on the bottom at all, " that they are in- 

 capable by their own unassisted efforts of raising the sand," and if 

 I understood him aright, bases his opinion upon the existence of 

 molluscs in the channel which could not live did the tides in any 

 way disturb the sands ! Curiously enough, I read in Nature (April 

 19th, p. 569) shortly afterwards that Major Reinhold, in a paper on 

 the botanical condition of the German Ocean read at a meeting 

 of the Natural History Society of Kiel, states that, according to 

 researches recently made, the Eastern part is almost wholly bare of 

 vegetation. "This is believed to be owing to the strong tidal 

 currents which so disturb the sea bottom as to prevent the germs 

 and spores of marine plants from settling." 



The Admiralty Chart of the English Channel shows a bottom in 

 many places composed of stones or gravel, or sand, stones and 

 gravel, at depths below the influence of wind waves ; so, if we accept 



1 Geol. Mag. April, 1890. 



