BRITISH ISLES. 23 



during the Secondary period ; but the author believes that the pent-up 

 volcanic forces manifested themselves in great and frequent oscillations 

 of level of the land, thus accounting for many anomalous characters 

 presented by the Secondary rocks of the district. Only small patches 

 of such rocks are preserved, these having been saved from denudation 

 by the protecting Tertiary volcanic sheets. 



Tables of the average composition of the Tertiary volcanic rocks are 

 given. The highly crystalline form of the acid series is granite, the 

 glassy form is obsidian ; the crystalline form of the basic series is 

 gabbro, the glassy form is tachylite : in each series there are numerous 

 intermediate varieties. The felspathic lavas have rarely extended more 

 than 10 miles from their points of eruption ; the basaltic lavas, how- 

 ever, have spread in vast sheets for 50 or 60 miles from their centres. 

 Both varieties assume columnar characters, the latter most strongly so. 



W. T. 



JuDD, J. W. Existence of Carboniferous Eocks in the Highlands of 

 Scotland. Geol. Mag. dec. 2, vol. i. pp. 573, 574. 



The author has found sandstone, shale, and coal, with Carboniferous 

 plants, near Morven, on the northern side of the Grampian axis. The 

 interest of the discoveiy lies : — 1st, in the proof of the great extension 

 of Carboniferous strata; 2nd, in the proof of enormous denudation 

 preceding the outpouring of the Tertiary lavas ; 3rd, in giving a base 

 to the series of PoikLLitic (Permian and Triassic) rocks of the High- 

 lands ; 4th, in adding another member to the series of rocks represented 

 in the Highlands, which now embraces representatives of all the great 

 geological formations except the Upper Siluiian. , W. T. 



Kerb, C. M. An Excursion of Mr. AVilson's Geological Class to 



Mount Sorrell. Rep. llugby School Nat. Hist. Soc. for 1873, 



pp. 7-9. 



The soil produced by the decomposition of the syenite was noticed 



to be thick ; and there is also Glacial Drift. Some of the sections are 



briefly noticed. W. W. 



KiNAHAN, G. H. On the Origin of the Lagoon called The Fleet, 

 Dorsetshire. Geol. Mag. dec. 2, vol. i. pp. 50, 51 ; see also Letters, 

 pp. 189, 239, 240. 



The author describes certain lagoons, marshes, and reclaimed lands 

 on the coast of Ireland. He believes them to have been formed as 

 foUows : — Tidal currents running nearly parallel to a coast-line, in 

 which there are rocks of unequal hardness, will denude the softer rocks 

 into bays ; shoals form between the headlands, due to the meeting of 

 currents of water in the bay with the water outside ; a slight rise of 

 the land will convert these shoals into bars with lagoons behind them. 

 Such, he believes, has been the origin of the Chosil Bank and the 

 Fleet. 



He thinks that shingle-beaches depend much on the tides, and but 

 little on prevailing winds, and supports liis arguments by examples 

 from the coast of Ireland. ^Y. T. 



