396 Scientific Intelligence — Geology. 



with feldstone-porphyry, and trappcan rocks. Above this, again, are 

 the Coniston limestone, the Ireleth slates, and several other depo- 

 sites, overlaid nnconformably by the old red conglomerate and car- 

 boniferous limestone. In reference to the classification of these 

 rocks, it is stated that good physical groups are the foundation of all 

 geology, and the most remarkable monuments of the past history of 

 our globe, so far as it is made out in any separate region. Organic 

 remains are, in the first instance, but accessaries to good sections ; 

 though, in comparing remote depositcs, they become the primary term 

 of comparison. The Coniston limestone and flagstone, in their lower 

 part, contain true Lower Silurian fossils ; all the higher part of the 

 series, till we touch the old red conglomerate, belongs to the Upper 

 Silurian system. The lower deposites, or the green slates and porphy- 

 ries, with the Skiddaw slates, are the true equivalents of the great 

 Cambrian group of North Wales. The latter, however, contains fossils 

 almost to its very base ; whereas the Cumberland beds have never 

 exhibited a single specimen. This rarity of organic remains may 

 have arisen from various causes ; but even in 1822, Professor Sedg- 

 wick pointed out the existence of carbon in these rocks ; and last 

 summer gave Mr J. Ruthven, of Kendal, directions to explore this 

 tract. His search has resulted in the discovery of two species of 

 graptolites, and some fucoids in the Skiddaw slate, which, conse- 

 quently, is not below the limits of organic life. These fossils belong 

 to the lowest groups ; and probably very nearly mark the limits 

 below which life has not extended. — AthcncRum,, No. 1061, p. 218. 

 February 26 18^8. 



15. Coral Island. — Although there is not much variety, there is 

 considerable beauty in a small coral reef when viewed from a ship's 

 mast-head at a short distance in clear weather. A small island, 

 with a white sand beach and a tuft of trees, is surrounded by a 

 symmetrically oval space of shallow water of a bright grass-green 

 colour, enclosed by a ring of glittering surf, as white as snow, im- 

 mediately outside of which is the rich dark-blue of deep water. All 

 the sea is perfectly clear from any mixture of sand or mud ; even 

 where it breaks on a mud beach, it retains its perfect purity, as the 

 large grains of coral are heavy, and do not break into mud, so that 

 if a bucket full of coral sand be thrown into the sea, it may be seen 

 gradually sinking like a white cloud, without producing any discolo- 

 ration in the surrounling water. It is this perfect clearness of the 

 water which renders navigation among coral reefs at all practicable, 

 as a shoal with even five fathoms water on it can be discerned at a 

 mile distance from a ship's mast-head in consequence of its greenish 

 hue contrasting with the blue of deep water. In seven fathoms 

 water, the bottom can still be discerned on looking over the side of 

 a boat, especially if it has patches of light coloured sand ; but in ten 

 fathoms the depth of colour can scarcely be distinguished from the 



