Mr. Prideaux on an undescrihed Substdphate of Iron. 397 



which occur in sea-sand, tertiary sand, and indeed in all mo- 

 dern formations, are viewed for the most part as different and 

 larger species, although of the same genera ; and it does no 

 appear that any of these forms can be referred with perfect 

 certainty to such as are now living in the sea. 



To the theory of the formation of limestone, the observation 

 is important, that these organic deeply-seated relations are 

 not peculiar to the chalk formation The tertiary calcareous 

 beds consist, in like manner with the chalk, of multitudes ot 

 such Polythalamian animals, which compose in many quarters 

 sandy sea-downs of great extent ; and even in the S'-^ndy^l^s^J-t 

 of Libya we can recognize distinct Polythalamia. On the 

 other hand, having succeeded in discovering microscopic 

 Polythalamia in the compact flints of the Jura limestone from 

 Cracow, which are of decidedly different forms from those 

 of the chalk, the calcareous animals being Nodosariaurceo- 

 lata, n. sp., and Soldania elegans, n. sp., and the siliceous 

 Puxidiculavriscal, Wx\h fragments of soft sponges, it becomes 

 apparent that such invisible organic bodies were also present 

 in the formation of the Jura limestone. 

 [To be continued.] 



LXIII Notice of an undescribed Native Subsidphafe of Iron 



from Chili. Bij John PraoEAUX, Esq* 

 npHIS specimen, of which I have not found any description, 

 A was brought to Sir Charles Lemon's Mining School by 

 Edward Hookham, one of the students, having been sent 

 from Chili to Captain N. Vivian, by his son, without any 

 ireological reference. • .\ ^c 



^ Form, mammillary, or curved lamelhar about one-sixth of 

 an inch thick. Structure, fibrous parallel, transverse to he 

 \t,m\uo^; fracture corresponding; fibres crystalline, but too 

 minute to^^be easily definable. Brittle in mass, fibres rathei 

 flexible. H 2-5 ; specific gravity below 2-5. 



are immediately dissolved. 



• Communicated by tii c Author. 



+ Dr. Bucklaud-s B.idgewater Treatise, 2nd Edition, vol. i. p. 448. 

 1837. Lyell's Elements of Geology, 1838. 



