254 



LYELL'S ELEMENTS OF GEOLOGY. 



Corals and Shells of the Mountain Limestone. 



general, more widely from living forms, some being generically 

 distinct from all those found in strata newer than the Coal. In 

 this number may be mentioned Orthoceras, a siphuncled and 

 chambered shell, like a Nautilus uncoiled and straightened- 

 Some species of this genus are several feet long (Figs. 266, 



Fig. 266. Fig. 257. 



Portion of Orthoceras lalerale, Phillips. O. giganteum. Sow. 



Mountain Limestone. Section showing the siphuncle 



reduced two-thirds. 



267.). The Goniatite is another genus nearly alh'ed to the Am- 

 monite, from which it differs in having the lobes of the septa free 

 from lateral denticulations, or crenatures ; so that the outHne of 

 these is continuous and uninterrupted (see ct, Fig. 268.). Their 



Fig. 268. ^ Fig. 269. 



Goniatites evolutus, Phillips.* Bellerophon costatus, Sow.f 



Mountain limestone. Mountain limestone. 



siphon is small, and in the form of the strise of growth they 

 resemble Nautili. Another extinct generic form of Cephalopod, 

 abounding in the Mountain limestone, and not found in strata of 

 later date, is the Bellerophon (Fig. 269.), of which the shell, 

 like the living Argonaut, was without chambers. 



Climate of the Carboniferous period. — The abundance of 

 lamelliferous and other corals, of large chambered Cephalopods 

 and Crinoidea, naturally leads us to infer that the waters of the 

 sea, at this period, were of a far warmer and more equable tem- 

 perature than is now experienced in those latitudes where the 

 Coal" strata abound, in Europe. M. Adolphe Brongniart has been 

 led to a similar conclusion in regard to the temperature of the 



* Phillips, Geoi. of Yorksh., pi. 20. fig. 65. 



tlbid.pl. 17. fig. 15. 



