REVIEWS 551 



The Beauforf s Dyke, off the Coast of the Mull of Galloway. By H 

 G. KiNAHAN. Proceedings of the Royal Irish Academy, 

 Third Series, Vol. VI, No. i. 



In the Proceedings of the Royal Irish Academy, Third Series, 

 Vol. VI, No. I, Mr. H. G. Kinahan, District Surveyor (Retired), H. M. 

 Geological Survey, describes "The Beaufort's Dyke, off the Coast of 

 the Mull of Galloway." This "dyke" is a deep trough in the bed of 

 the Irish Sea nearer the coast of Scotland. The plate accompanying 

 the article reproduced from the Admiralty charts, shows a long line of 

 soundings of 100 to 148 fathoms, surrounded by a comparatively level 

 bottom 70 or 80 fathoms deep. Attention is just now directed to 

 these depths by the proposition to construct a tunnel from Scotland to 

 Ireland. The geological interest lies in the fact that in this trough 

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

 144 fathoms that are carried backward and forward similarly to those 

 on an ordinary sea beach." This is much deeper than the waves and 

 currents even on most exposed coasts have been supposed to act. The 

 vigor with which this deep washing occurs maybe inferred from figures 

 given in a table, which show that at one point the bottom was cut 

 down by erosion from a depth of 1 1 7 fathoms to a depth of 146 fathoms 

 from 1894 to 1897 or nearly 60 feet a year. At other times filling was 

 similarly rapid. The origin of the dyke or trough itself is left in doubt 

 but faulting and glacial action are suggested. The origin of currents 

 capable of acting at that depth is the main subject of interest. It is 

 assumed that while the effect of wind waves and tide waves is reduced 

 to zero at moderate depths there are deep currents induced by these 

 superficial waves, to the depth of whose action no definite limit is 

 assigned. The author contrasts these currents with the ordinary tidal 

 races which may be supposed to erode shallow places more than deep 

 ones. He refers to his former publications for detailed proof that 

 denudation by these currents in question "is in ratio to the depth of 

 the water." The whole article goes to show that when the movements 

 of water are controlled by channels or reflected from irregular shores, 

 the coarseness of the sediments at given depths bears little relation to 

 the mathematically computed power of the water for those depths. 



N. M. F. 



