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PALJEOZOIC ROCKS OF THE BRITISH ISLES. 



Silurian Hocks. — In the Address of last year I plainly expressed 

 my belief, founded not merely on researches in the British Isles, but 

 also on examinations of large portions of the Continent, that the 

 Lower Silurian group contained the most ancient fossiliferous type. 

 This view now rests upon still firmer support, established by the 

 labours of our geologists at home, and the doubts respecting the 

 true zoological base of the Palaeozoic rocks have been entirely dis- 

 pelled. In South Wales this point has been worked out with extra- 

 ordinary fidelity of research, founded both on geometrical measure- 

 ments and a close search after fossils; and to these investigations I will 

 presently advert, when speaking of the labours of Sir Henry de la 

 Beche and his assistants of the Ordnance Geological Survey. 



In illustration of the structure of the Lake Country of the North 

 of England, Professor Sedgwick has recently given a short sketch 

 in three letters addressed to Mr. Wordsworth ; and I beg you to 

 consult this little work, which is embodied in a Guide to the Lakes 

 published by his friend the celebrated poet, both as a specimen of 

 the author's vigorous style of communicating popular geological 

 knowledge, and to obtain from it a clear general perception of the 

 configuration of that remarkable region, and of the changes it has 

 undergone. In regard to the older Palaeozoic rocks, referring to a 

 memoir which he read before this Society in 1832, he still adheres 

 to the threefold division of the slate-rocks of Cumberland proposed 

 by Mr. Jonathan Otley. With the two lowest of these, the Skiddaw 

 slate and the green slate and its associated porphyry, we need not 

 now concern ourselves, for they contain no organic remains. The 

 third division, or the Upper Slaty rocks, is considered by Professor 

 Sedgwick to represent the Silurian series. He separates it into three 

 groups, the uppermost of which he compares with the Ludlow rocks, 

 the second is an ill-defined hard siliceous mass, with no good fossils, 

 and the lowest consisting of the Ireleth slate and limestone, inclu- 

 ding the Coniston, is proved by its fossils to be of the age of the Lower 

 Silurian rocks. This view is, in short, that which has been for some 

 time entertained by Professor Sedgwick*, and is essentially the same 

 as that taken by Mr. James Marshall. 



During the preceding year our attention was also attracted to the 

 district by the labours of Mr. Daniel Sharpe, who had commenced a 

 more detailed inquiry into the subdivisions of this series. He has 

 since presented us with the results of additional researches made 

 during the last summer, which have led to some corrections of the 

 Map formerly prepared, and to some changes in lines of fault as Avell 

 as in the order and subdivision of the stratified masses. Describing 

 the formations in ascending order, he enumerates several additional 

 Lower Silurian fossils as occupying the Lower Coniston limestone 

 with its overlying series of shale, slate and flagstone ; and he amends 

 the arrangement which he proposed last year, by also including in 

 the Lower Silurian division certain grey slaty greywacke grits 

 which he had left in the undefined group called by him " Winder- 

 * See Proceedings Geol. Society. Vol. iii. p. 545 et seq. 



