Feathcrstonhaugh^s Geological Report. 35 



earthy limestone. The several species of fossils are phrag- 

 moceras a new genus, asaphus, two species of cardiola, (a new 

 genus,) nautilus, spirulites, pentamerus, pleurotomaria, ortho- 

 cera, &c. ; most of them new species. 



These beds are separated from the upper ones by a sub- 

 crystalliae gray and blue argillaceous limestone, containing 

 pentamerus, pileopsis, bellerophon, lingula, atrypa, terebra- 

 tula, calamopora, and some other fossil corals. The upper 

 beds are a slightly-micaceous, gray-colored, thin-bedded sand- 

 stone, containing avicula, atrypa, cypricardia, homonolotus, 

 (a new genus,) leptsena, orthis, orbicula, orthocera, pleuroto- 

 maria, turbo, with gigantic serpentine bodies, &c.* 



It sometimes occurs that the zones of limestone which sepa- 

 rate the Wenlock and Ludlow divisions thin out and disap- 

 pear : in such cases, the characteristic division being lost, Mr. 

 Murchison calls the united mass u the upper Silurian rocks ;" 

 and where the same characteristic division between the Llan- 

 deilo and Caradoc beds disappears, their united mass is termed 

 the " lower Silurian rocks." 



It will be perceived that the formations which have been 

 briefly described comprehend all the deposites lying between 

 the old red sandstone and the primordial rocks, and that some 

 of them must necessarily be the equivalents of those grauwacke 

 rocks which, in all the hitherto published geological treatises, 

 figure so conspicuously, but in a very undefined manner, as 

 immediately subjacent to the old red sandstone, which last, 

 notwithstanding its vast bulk, has been considered by an ex- 

 perienced and popular geological writerf as a true grau- 



* Mr. Murchisor.'s Fossils of the Silurian System, when published, will add 

 weight to the opinion expressed in my report of 1835, of the " great uni- 

 formity of the genera in the inferior rocks of both hemispheres." He has 

 compared some of the fossils of this country with those of his Silurian system, 

 and says, in a late letter, " many of your organic remains are specifically 

 identical." 



f Bakewell. 



3* 



