726 Mr. Lonsdale on the Age of the 



tion class, it was far more justifiable to adopt the view put forth in Mr. De la 

 Beche's paper, and to assume that the new species were only a legitimate 

 addition to the Fauna of the mountain-limestone, than that they marked a 

 distinct period of organic life. (Geol. Trans., 2nd Series, vol. iii. p. 164.) 



Mr. Phillips's lists of fossils in the Encyclopaedia Metropolitana were espe- 

 cially valuable, when published, by giving- the foreign and British localities at 

 which each species was considered to have been found. The list assigned 

 to the transition series contains thirty-eight species of Devonshire shells, eleven 

 of which are shown to occur also at PaffVath, Bensberg, the Eifel, and in Goth- 

 land, then considered true greyvvacke or transition districts below the old 

 red sandstone. It is worthy of remark, however, that only three species, 

 Producta depressa, Terehratula affinis, and Orthoceras circular e, are stated 

 to be found at Dudley or Ledbury ; one, Pileopsis vetusta, near Ludlow ; and 

 one. Cirrus acutus, at Tortvvorth ; and no other English transition localities 

 are mentioned. Twenty-one of the Devonshire shells are further marked as 

 common to the transition and carboniferous systems ; and Mr. Phillips, with 

 a just view of the tendency of this evidence, remarks, " We must leave it to 

 future observers to say whether it is quite certain that the limestones of De- 

 vonshire really belong to the transition series, a point on which we cannot 

 avoid feeling some doubt." (Encyc. Metrop., p. 573-577.) 



At that time Mr. Murchison's Silurian System was not published, and Mr. 

 Phillips had therefore only one of the two terms of comparison necessary 

 for establishing the true age of the limestones. He had also a knowledge of 

 only a part of the fossils of the county. If he had been supplied with these 

 requisites for forming a right judgement, who can doubt the result ? 



In dwelling for a moment on the attempts to define the age of the lime- 

 stone, it is curious to perceive how the opinion of the same observer has occa- 

 sionally oscillated between the mountain-limestone and the upper portions of 

 the transition series ; in consequence, no doubt, of the want of that prepon- 

 derating weight of evidence which is necessary to satisfy the mind of the 

 practical workman, and enable it to rest steadily on its own decisions. If it 

 should be considered that a better result is now attainable, it must be remem- 

 bered that a great amount of evidence has been lately accumulated, not in 

 Devonshire only, but in other and distant parts of the kingdom. Until the 

 organic remains of the mountain-limestone and of the Silurian system had 

 been determined, it was vain to speculate on the age of a series of fossils, 

 procured from a region but partially examined, beset with faults, and tra- 

 versed by igneous rocks. 



I will now state briefly the zoological evidence on which I assumed that 



