M. Damour on the Composition of Nullipores. 87 



cisely on those places where the shock of the waves is fult most 

 Btroncrly. The numbers 4 and 5, from the collection of the Museum, 

 were sent to the author by M. Decaisne. It is to be remarked, that 

 the two last contain mere traces of carbonate of magnesia, whilst 

 the four others contain from 8^ to 17 per cent, of this carbonate. 

 In fact, the numbers 6 and 6 belong to families which are very 

 distinct from the preceding. The earthy matter which covers them 

 does not penetrate to the interior of the plant. The numbers 1, 2, 

 3, and 4, are intimately penetrated with calcareous and magnesian 

 matter. 



The foregoing analyses seem to indicate that the groups of Coral- 

 linacese act the same part in the vegetable kingdom that the Polypi 

 and the greater part of the MoUusks do in the animal kingdom. By 

 means of their organisation, these plants have the faculty of decom- 

 posing the water of the ocean, and to extract, secrete, and incorpo- 

 rate principally lime and magnesia converted into carbonate. The 

 development of these vegetables on certain coasts and in low lands, 

 and consequently the deposits of magnesian limestone which they 

 must occasion, seem also deserving of consideration in the study of 

 geological formations. — Comptes Rendus, Fevrier 1851. — The Phi- 

 losophical Magazine y 4th series, vol. i. No. 5. May 1851, p. 434. 



Note on an Incrustation of Black Oxide of Manganese. By 

 John Davy, M.D., F.R.S., &c. Communicated by the 

 Author. 



In the Lake District of Westmoreland and Cumberland, 

 pebbles and water-worn stones, coloured black, either with 

 or without lustre, are not of uncommon occurrence in the 

 beds of the moorland and mountain streams, or in the allu- 

 vium of the lower valleys excavated by the wasting action of 

 torrents. When minutely inspected, the colouring matter is 

 found to be superficial and independent of the kind of stone 

 that exhibits it, — some of the pebbles thus coloured being of 

 quartz, others and the greater number of the prevailing rock 

 of the country, varieties of clay slate, more or less indurated 

 and changed. The lustrous specimens are not unlike nodules 

 of plumbago ; those destitute of lustre are of an opaque 

 black resembling that of the black oxide of manganese in a 

 pulverulent state. On examination, I have found the colouring 

 matter of both to consist of this oxide. It imparts the same 

 brown stain when rubbed on paper or on the hand ; and chlo- 



