128 M. Eicliwaltrs Geological Remarks upon the 



lies another containing fossils, and of peculiar texture It is 

 compact and firm. The shells appear here changed into a blu- 

 ish calcareous spar, and some oxide of iron is found collected in 

 the cavities. Upon this there rests another more compact lime- 

 stone of a fine grained texture, and with fewer traces of fossil shells. 

 Over this last there follows a limestone which is completely por- 

 ous, and almost of the nature of sinter ; it is traversed by very 

 large holes, which appear to be occasioned by fossil tubes of Ser~ 

 puhe. These holes are often a quarter of an inch thick ; but 

 are mostly much thinner, and are formed of the same yellowish 

 calcshiter. Likewise there are found SerpulcB tubes, which are 

 scarcely half a line thick ; they are formed of a very thin and 

 friable white calcareous mass, and lie grouped together in the 

 hollow cavities of the limestone. As to their species, they are 

 evidently different from the SerpuloR, resembling Planorbts, of 

 the east coast near Tjukkaragan, since they appear much 

 longer, and very irregularly rolled up ; so that they seem to 

 be much nearer the fossil Serpula of Volhynia. The porous 

 limestone consists throughout of tolerably large particles, and 

 shews that it has exactly the structure of tuff; so that a mass 

 of this same species, lying over the former shell limestone, 

 would be proved to have been formed at a very late date. 

 There next rests upon this another limestone which does not 

 contain petrifactions ; upon this again is found a layer of loose 

 sand, the quartz particles of which appear fine, and of a 

 yellowish colour. This layer is not more than one foot thick. 

 Upon this sand there lies a calcareous marl, of a blackish- 

 grey colour and firm texture. It is placed horizontally like 

 all the superimposed and subjacent formations here> and springs 

 readily into square fragments. Farther, upon this last there 

 lies limestone, which, however, is not purely calcareous, but 

 contains within it particles of quartz. There are likewise found 

 in it, sometimes, cavities with crystallized calcareous spar. 

 Towards the upper part it passes into stratiform sandstone, 

 which again is calcareous. This contains the same sort of 

 quartz grains as the underlying loose sand. Upcm this last 

 there follows anew a compact limestone without shells ; but upon 

 this there is a shell-limestone, like that mentioned above, of a 

 yellow or even of a grey colour : it contains shells broken into 



