74 REPORT — 1875. 



Observations on the Discovery, by Count Abbot Castracane, of Diatoraacece in Coal 

 from Lancashire and other places*. By Prof. Edavakd Hull, F.B.S. 



The author considered this discovery of so much interest and importance as to 

 entitle it to the special notice of the Section, and particularly for the light it throwa 

 on the mode of formation of Carboniferous coal. Diatoms had been observed by 

 Count Castracane in specimens of coal from Liverpool, Newcastle, Scotland, and 

 St. Etienne ; and in these, after repeated observations in which every precaution 

 had been taken to guard against deception, examples had been found in greater or 

 less numbers. The species observed are identified by Count Castracane with ex- 

 isting forms, and, with the exception of tliree maiiue genera from the coal of 

 Lancashire, were all of freshwater origin. The results appeared to the author to 

 corroborate the views of those who consider that Carboniferous coal had its source 

 in the decay of forests of plants, which gi'ew with their roots and parts of their 

 stems under stagnant lagoons, into which the waters of the ocean occasionally 

 found access. 



The Dnfting-power of Tidal Currents and that of Wind-waves\. 

 By G. Henry Kinahan, M.B.I. A. ^-c. 



The author referred to the Report on Waves by J. Scott Rus.sell (Brit. Assoc. 

 Reports', vol. xiii. 1844, p. 311), which he considered ought to have decided the 

 relative merits of the tidal currents and wind-waves. This, however, seems not 

 to be the case, judging from the recent paper on the Chesil bank, Dorsetshire, read 

 by Professor Prestwich before the Institution of Civil Engineers (February 2nd, 

 1875), and the discussion that followed the reading of it. 



After mentioning what can be learned from Scott Russell's Report, the author 

 gives the general conclusions he arrived at, after many years of the study of the 

 driftiug-power of the tidal currents and that of wind-waves on the coast of Ireland ; 

 and to illustrate these general conclusions, a detailed description was given of that 

 portion of the coast of Ireland (part of AVicklow, Wexford, and Waterford) con- 

 tained in the Admiralty charts (Ireland, sheets xiv. & xv.), as this coast was 

 aninutely examined and the results tabulated. 



Tile memoir concluded as follows. The information gathered on this portion of 

 tlie coast of Ireland goes to prove the following : — 



1st. The driftage due to tlie incoming tidal currents is alwaj-s, during its 

 progress, goingon in deep water, and more or less in the shallow water. 



2ud. The driftage due to wiud-waAes only occurs dui-ing gales, and even then 

 is only due to the waves that break on the shores. 



•Ji'd. To prevent the tidal driftage, groins or piers should be erected ; and if 

 the pier is to form a harbour, transverse groins should run out from it to stop the 

 back-wash generated by the piers; for otherwise this back-wash would cany the 

 driftage seaward to be sucked round tlie pier into the harbour. 



4th. As the wind-wave driftage occurs during gales, and then only on the 

 shore-line, it might be prevented from silting up a harbour or damaging the ship- 

 ping in it by placing a breakwater across the direction from wliicli the prevailing 

 storms come. If sucli a breakwater were a fixed one, built of stone or some such, 

 it must more or less aiiect the tidal diiftage, and probably would help to silt up the 

 harbour ; but if it were floating, it would break the wind-waves in deep water, 

 thus destroyino- theii- drif ting-powers, wliile there would be no impediment to inter- 

 fere with the tidal driftage. 



On the Limits of the Yoredale Series in the North of England. 

 By G. A. Leboue, P.G.S. c|y-. 



The author urged that the Great ^N'liin-Sill, being an intrusive sheet of trap 

 which shifted its horizon frequently in Northumberland, was worthless as a base- 



* Atti dell' Accad. Pout, de' Nuovi Lincei. Eoiiia, 1874. A translation of the memoir, 

 by Miss Littledale, of Dublin, appears in the Geol. Mug., Sept. 1875. 

 t See ' Royal Irish Academy Proceedings,' 1875-76. 



