is tmporlanl to the Progress of Geology, 279 



it IS most desirable for the interests of Science, that they should 

 «o accumulate, as the only means of enabling him to deduce the 

 true characters and nice d'islinctiovs wlnck are necessary in de- 

 scribing Fossil Shells, so as to render the same useful in Geo- 

 logical investigation. 



It remains for me to mention one other very important cau- 

 tion to Collectors of Fossil Shells and mineral matters, which is 

 rendered necessary, l)y the almost universal scatter of alluvial 

 rulh't'ih on the tops of the regular and undisturbed Strata, such 

 alluvium being often accunmlated to a vast thickness, of alluvial 

 Clay in particular, and in which, as well as in alluvial Sand, and 

 the more obviously worn Gravels, foss-il shells are commonly 

 found, mostly in a worn state, but not invariably so. The care- 

 ful Observer need in no instance to be in doubt, as to distin- 

 guishing alluvium from strata, if he will attend to the regularly 

 laminated and unmixed nature of the latter, except as to grains 

 they may be composed of (as Sand, Sandstone, &c.) or nodular 

 masses, (like those of Flint, Ironstone, Sic.) and organized remains 

 they may contain, which are regularly disposed in strata, in most 

 instances; while on the contrary^ the alluvial matters, always found 

 upon and never under any regular stratum ,?Lre disorderly mixtures, 

 containing jvaler-worn and violently hro/ien pebbles and stones, 

 most of them entirely foreign to the district in which they now 

 lie, and which may, some of them, have come from the antipodes, 

 for aught that has yet appeared to the contrary: there is like- 

 wise an intermediate class of loosened substances fotmd, either 

 under f he gravels and other alluvia, or nearly naked on the surface, 

 which is called Rubble, Ramel, Stone-brach, &c. in different 

 districts, consisting for the most part of angular and unworn 

 fragments of the stoney stratum or Rock immediately beneath, 

 merely loosened up, sometimes without the intervention of any 

 extraneous matters between these small loosened stones, but more 

 commonly, some of the loosened matter of the next superior stra- 

 tum of the series, and more rarely, gravel-stones, alluvial-shells, &c. 

 liave fallen in among these Rubbles : — on all these accounts, the 

 caution I have mentioned is abundantlv necessary, always to note 

 it on the spot, where fossil shells were found in the alluvium, and 

 to call these alluvial shells: — of which latter class, any particular 

 specimen may appear to be unique in the district wiiere it is 

 found, which in reality is no m.ore so, than the finding of a single 

 Oyster, Cockle or Muscle Shell, in ploughing a Field, carried 

 thither in the manure, after having been brought from the Sea 

 by Man, would entitle this shell to such a character of rarity. 



Hoping that I shall ere long see an increase of Communica- 

 tiwns, from Men practically concerned and versant in the mineral 



S -J concerns 



