System cannot be of the age of the Old Red Sandstone. 119 



Conchifera Brachiopoda ... 83 Mountain Lime 21 

 Gasteropoda 36 8 



Cephalopoda Monothalamacea 7 3 



Polythalamacea ■i^ 8 



Crustacea 9 1 



Here we have presented to us the strange anomaly of the 

 Poli/piaria, a class of creatures which have the widest distri- 

 bution of any, and are apparently constituted better than any 

 to resist physical mutations and local accidents, being nearly 

 annihilated by conditions under which 25 per cent, of the 

 higher orders o^Brachiopoda andG aster opoda flourished, while 

 the Crinoidea could only exist in a like proportion with the 

 latter. 



If we refer to the class Crustacea^ the Devonian species 

 bear the same proportion to the Silurian as to the mountain 

 limestone, one and one. So that according to the Old Red 

 supposition, these creatures were universally effaced in the 

 ratio of 36 for every one which survived ; effaced too during 

 the short intermediate interval implied in the upper Ludlow 

 rocks. If, however, we regard the aggregate amount of species, 

 the Silurian exceeds the Devonian by something moi'e than 

 four times, viz. 37 to 9, and exceeds the Carboniferous as 

 37 to 10. So that looking at the Trilobites as a family, they 

 appear rather to have been introduced in an advanced period 

 of the Devonian epoch, to have flourished by myriads in the 

 meridian of the Silurian, and to have died out in the Carboni- 

 ferous. 



Mr. Lonsdale's table gives 1 1 species as mountain lime, 

 13 as Silurian, and not one as Old Red Sandstone out of 40 

 figured by Mr. Murchison. The Table comprises 62 species, 

 collected from the upper strata of the Devonian rocks, and 

 therefore, according to the imaginary Old Red equivalence, 

 vei-ging on the confines of the mountain limestone ; for I re- 

 peat it as a fact which can never be disproved, that some of the 

 South Devon limestones are included in the floriferous series, 

 while others with the killas overlie it. Mr. Lonsdale's list 

 does not include one mountain lime coral, while 8 out of 19 

 are Silurian ; so that, according to that enumeration, the dipper 

 Devonian approximates rather to the Silurian than to the 

 Carboniterous system, and, in truth, rather shows the Silurian 

 to be the intermediate formation than as Mr. Lonsdale puts it, 

 Mr. Lonsdale however relieves himself from this untoward 

 result, by pretty broadly stating that " Professor Sedgwick 

 and Mr. Murchison have proved lor the first time that the 

 culm-measures of the central part of Devon are newer than 

 any of the stratified groups associated with them, and of the 



