78 Colonel Silvertop on the Lacustrine Basins of 



charged with the latter in some places, as to pass into an imperfect 

 lignite. With these layers, which may be followed for a consi- 

 derable distance by the eye, until they successively become 

 concealed by the intersection of the rising bed of the ravine, 

 there is associated a remarkably fine white sand, formed of mi- 

 nute grains of transparent quartz ; the layers are from one to 

 two inches thick, of a leafy structure, and so extremely friable, 

 that it is nearly impossible to detach an entire specimen, as it 

 falls to pieces between the fingers. They are full of planorbes 

 lying horizontally upon the surface of each successive leaf or 

 plate of the layer ; but the shells, although frequently retaining 

 a nacreous lustre, are in a decomposing state, and rarely entire, 

 so that every new exposed surface is studded with their frag- 

 ments, or marked by their impressions. 



The associated sand forms no regular stratum or continuous 

 bed, but it is generally seen in more or less abundance, loosely 

 attached to the surface of each layer. A bed of brown coal, of 

 unknown depth, immediately succeeds in a descending series, 

 and in its superior part, or that contiguous to the former, I also 

 observed quartzose sand under similar circumstances. This 

 brown coal is of a dullish-black colour, and in horizontal divi- 

 sions, from one to four inches thick. The thinner ones, how-. 

 ever, both superficially and in a cross fracture, sometimes exhi- 

 bit a shining and even surface ; but in the thicker strata or di- 

 visions, the fracture is uneven, and dull. On the surface of a 

 specimen of the latter in my possession, taken from the superior 

 part of the bed, there are innumerable fragments of planorbes. 

 As it is in the lowest part of the banks of the ravine that this 

 bed of brown coal begins to take a decided character, no means 

 are afforded of examining the interior of the mass ; and the 

 workings undertaken here some years ago, under the idea that 

 it was the real coal, by the proprietors of a sugar manufactory 

 at Torroz, on the Mediterranean coast, arfe unfortunately obli- 

 terated. 



The ravine in which the appearances just sketched may be 

 seen, only penetrates the ridge for about two hundred yards ; 

 but as some strata of a similar nature are observed on the banks 

 of the stream, on its opposite side, it appears probable that this 

 bed occupies its whole breadth. 



