338 . Intelligence and Miscellaneous Ar ticks, r - 



bably the result of the decomposition of eopper-ores, and has been 

 formed subsequently to the crystals of lime in the limestone, which 

 are often tipped with an octahedron of ruby oxide, or overlaid with 

 spikes of the native copper. 



5. " On the Slate-rocks and Trap-veins of Easdale and Oban." 

 By Professor James Nicol, F.G.S. 



The author first described the mineral characters of the clay- slate 

 of the Islands of Easdale and Seil, and noticed the iron-pyrites and 

 the veins of calc-spar and of quartz occurring in the slate, as well 

 as the gritty and calcareous strata that are detected as interstra- 

 tified with the more highly cleaved beds of the slate ; also some soft 

 carbonaceous beds and some hard calcareous nodules, imbedded in 

 the slate. In one of these nodular masses, at a depth of 140 feet 

 from the surface, a small quantity of bituminous coal was stated to 

 have been lately found. Fucoidal or annelidal markings occa- 

 sionally appear in the slates. Prof. Nicol then described the ori- 

 ginal but obscure stratification of the Easdale slate, which, with 

 care, is seen to present beds disposed in undulations, and, where 

 most clearly seen, dip at a high angle to the west or north-west. 

 Near Oban, and along the Sound of Kerrera, the stratification is 

 more distinct, and the strata are very much contorted. The slaty 

 cleavage of the district was then treated of in detail. Its average 

 strike varies 20° from that of the beds ; and the direction of strata 

 and cleavage-planes have evidently a connexion with the more 

 ancient and deep-seated causes which have produced the most 

 striking features in the configuration of the country ; they are nearly 

 parallel to the shores of Loch Linnhe, to the Island of Lismore, and to 

 the great depressions occupied by Loch Etive, Loch Awe, and Loch 

 Fyne. The trap-veins of Easdale and Oban were next described, 

 especially a pitch-stone on Seil, and were shown to be of three 

 periods. At least two sets of the veins appear to be of a date sub- 

 sequent to the Jurassic period ; and the author remarked, as an in- 

 stance of the very recent date of many of the great convulsions by 

 which the present physical outline of Scotland has been produced, 

 that the mountain- cliiF, 1200 to 1500 feet high, forming the coast 

 of Morne, between Ardtornish and Loch Linnhe, consists in half 

 of the old gneiss, in half of lias-strata and recent trap, brought side 

 by side with each other along an enormous fault, and now smoothed 

 down into one uniform mass. In conclusion. Prof. Nicol stated 

 that he considered the Easdale slate to be of Lower Silurian age, 

 but younger than the slates of Birnam and Dunkeld. 



XXV. Intelligence and Miscellaneous Articles. 



RESISTANCE OF SHIPS. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN the course of last year there were communicated to me in con- 

 fidence the results of a great body of experiments on the engine 

 power required to propel steam-ships of various sizes and figures at 



