KiNAHAN — Bemiforfs Dyhe, coast of the Mull of Galloway. 27 



insisted that tidal and wind waves were inoperative below very 

 limited depths. This subject was studied during a series of years 

 by the writer, who proved, by indisputable evidence, that the actions 

 of the currents, due to the combination of tidal and wind Avaves, 

 was much deeper than was supposed. 



The results of these inquiries have appeared in the Publications 

 of this Academy, the Institutions of Civil Engineers, England and 

 Ireland, and in those of the Geological Societies of England, Ireland, 

 Edinburgh, Glasgow, Manchester, etc. 



The earlier observers may be excused, as it was then generally 

 believed, that the greatest denudation took place at low water. This 

 supposition was very excusable, as it would appear obvious that 

 tidal currents have more effect at low- water than previously. Now, 

 however, it is known that the greater the depth of the water, the 

 greater the force ; consequently the greatest denudation takes place at 

 the high- water of the spring-tides — that is, the denudation is in ratio 

 to the depth of the water. To go fully into this su.bject would 

 occupy a considerable space : we may, therefore, take it as proved, 

 and refer those interested to the reports on the subject. It can, 

 however, be seen that this being proved, the original ideas on tidal 

 denudation and effects must be considerably modified ; more especially 

 as the travelling-sands, gravels, and their adjuncts, in the "Beaufort's 

 Dyke," show conditions that vary from any previous records, as there 

 are sands, gravels, and their adjuncts, at depths of from 120 to 

 144 fathoms (600 to 864 feet in that place), that are carried backward 

 and forward similarly to those on an ordinary sea-beach. 



The early surveyors used sounding-lines of limited lengths, so 

 that, on their charts, all exceptional deeps are unrecorded ; we there- 

 fore cannot give the early history of the "Beaufort's Dyke," as no 

 chart could be found in which these depths are recorded earlier than 

 1867. The next chart is dated 1879 ; then we have one in 1885, and 

 others in 1890, 1894, 1897, and 1898. The map lately published in 

 the Daily Graphic seems to have been made from the soundings taken 

 early in either 1897 or 1898, but there is no chart now to be bought 

 sbowing a similar outline. From the 1897 chart, we learn that then 

 the gulch forked to the northward, and had lessened in that direction : 

 it had also shoaled-up very much ; while south-east of the Bill of the 

 Mull, there was a remarkable deep of over 120 fathoms. Shoaling-up 

 seems also to have taken place in 1879; while in 1869 the gulch 

 was cleared in a great measure of the sands and their adjuncts. 

 When the 1897 chart was made, the shallow in the gulch was on a line 



