94 On Blackheath Pebble-bed, and on certain Phenomena 



column of remarks, " Fine weather, every appearance of trades — ba- 

 rometer up." This remark is made the 5th March 1850, in 6° south 

 lat. Had he passed this cloud-ring in August, he would probably 

 have made the same observations in 6° north lat., indicating that he 

 had passed from under the influence of this equatorial cloud-belt. 



It is thus we arrive at a new application of the barometer, which 

 thus informs the navigator, when other means fail, when he leaves 

 and when he enters the trade-winds. 



On the Blackheath Pebble-bed, and on certain Phenomena 

 in the Geology of the Neighbourhood of London. By Sir 

 Charles Lyell.* 



There are two kinds of flint-gravel used for making roads in the 

 neighbourhood of London, both of them in certain places superficial, 

 but which are of extremely different ages. The yellow gravel of 

 Hyde Park and Kensington so often found covering the " London 

 Clay" may be taken as an example of one kind ; that of Blackheath, 

 of the other. The first of these is, comparatively speaking, of very 

 moderate date, and consists of slightly rolled, and, for the most part, 

 angular fragments, in which portions of the white opaque coating of 

 the original chalk flint remain unremoved. The more ancient gravel 

 consists of black and well-rounded pebbles, egg-shaped or spherical, 

 of various sizes, exhibiting no vestige of the white coating of the ori- 

 ginal flints, yet shewing by the fossil sponges and shells contained in 

 them that they are derived from the Chalk. In the pits of Black- 

 heath and the neighbourhood, where this old shingle attains at some 

 points a thickness of 50 feet, small pieces of white chalk sometimes 

 occur, though very rarely intermixed with the pebbles. If we meet 

 with thoroughly rounded flints in the more modern, or angular 

 gravel, it is because the latter has been in part derived from the de- 

 nudation of the older bed. 



The researches of the Rev. H. M. De la Condamine have shewn 

 that the sand and pebble -beds of Blackheath and Greenwich Park 

 inclose in some of their numerous layers fresh-water shells of extinct 

 species, such as Cyrena cuneiformis, &c, agreeing with fossils which 

 characterise the Lower Eocene beds at Woolwich. At Lewisham 

 the pebble-bed passes under the London Clay, and at Shooter's Hill 

 this clay overlies it in great thickness. 



At New Charlton, in the suburbs of Woolwich, Mr De la Conda- 

 mine discovered a few years ago a layer of sand in the midst of the 

 pebble-bed, where numerous individuals of the Cyrena tellinella 

 were seen standing endwise, with both their valves united, the pos- 

 terior extremity of each shell being uppermost, as would happen if 

 the molluscs had died in their natural position. Sir Charles Lyell 



* Read in Royal Institution of Great Britain, on April 1, 1852. 



