Cn. XXVII.] CAMBRIAN GROUP. 447 



quite unfounded, geographical provinces having evidently existed in the 

 oldest as in the most modern times.* 



Whether the Silurian rocks are of deep-water origin. — The grounds 

 relied upon by Professor E. Forbes for inferring that the larger part of the 

 Silurian Fauna is indicative of a sea more than 70 fathoms deep, are the 

 following : first, the small size of the greater number of conchifera ; 

 secondly, the paucity of pectinibranchiata (or spiral univalves) ; thirdly, 

 the great number of floaters, such as Bellerophon, Orthoceras, &c. ; 

 fourthly, the abundance of orthidiform brachiopoda ; fifthly, the absence 

 or great rarity of fossil fish. 



It is doubtless true that, some living Terebratulce, on the coast of Aus- 

 tralia, inhabit shallow water ; but all the known species, allied in form to 

 the extinct Orthis, inhabit the depths of the sea. It should also be re- 

 marked that Mr. Forbes, in advocating these views, was well aware of the 

 existence of shores, bounding the Silurian sea in Shropshire, and of the 

 occurrence of littoral species of this early date in the northern hemisphere. 

 Such facts are not inconsistent with his theory ; for he has shown, in 

 another work, how, on the. coast of Lycia, deep-sea strata are at present 

 forming in the Mediterranean, in the vicinity of high and steep land. 



Had we discovered the ancient delta of some large Silurian river, we 

 should doubtless have known more of the shallow-water, brackish- water, 

 and fluviatile animals, and of the terrestrial flora of the period under con- 

 sideration. To assume . that there were no such deltas in the Silurian 

 world, would be almost as gratuitous an hypothesis, as for the inhabitants 

 of the coral islands of the Pacific to indulge in a similar generalization 

 respecting the actual condition of the globe. 



CAMBRIAN GROUP. 



Upper Cambrian. — We have next to consider the fossiliferous strata 

 that occupy a lower position than the " Llandeilo beds," which last form, 

 as we have seen, the Lower division of the great Silurian series, as origi- 

 nally defined by Sir R. Murchison. In the Appendix to his important 

 work before cited,f Sir Roderick has given, on the authority of Mr. Salter, 

 a list of no less than 96"species of fossils (of which specimens have been 

 examined either by himself or Professor McCoy), all common to the 

 Upper and Lower Silurian strata, or, in other words, which, being found 

 either in the Ludlow or Wenlock beds, are also met with in the Llandeilo 

 formation. The range upwards of so many species from the inferior to 

 the superior group shows that, independently of the link supplied by the 

 Caradoc or Middle Silurian, there is such a connection between the two 

 principal divisions, as makes it natural to assign the whole to one great 

 period. To attempt, therefore, to give a new name to the Llandeilo beds, 

 or to call them Cambrian, as has been recently proposed by some geol- 

 ogists, would be to act in violation of the ordinary rules of classifica- 



* E. Forbes, Anniv. Address, 1854, Quart. Journ. Geol. Soc. voLx. p. 88. 

 f Siluria, p. 485. 



