THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 185 



Ctenodonta sp. The fossil from Gorran Haven now in the Jermyn 

 Street Museum and labelled Arenig may be a new 

 species. The only Llandetlo species of which we are 

 aware occurs in the Llandeilo Flags. It is named on 

 the authority of Major Wyatt-Edgell. 



Orthoceras cylindraceum is probably not the fossil now described 

 under that name, which is typical Upper Devonian and 

 Lower Carhoniferous. The specimens so named may be 

 imperfect. 



0. encrinale, a Llandeilo species. 



0. gracilis of Mc Coy is said to have been found ' ' in the rocks 

 to the S. of St. Austell." This is too vague to be of 

 any value for our present purpose. 



Loxonema lineata, mentioned by Murchison, 1846, is perhaps some 

 smooth species of Murchisonia, such as the M. gracilis, 

 which is Llandeilo, or perhaps it is a Holopella. The 

 later editions of ''Siluria" do not mention any Lower 

 Silurian species of Loxonema. 



On the whole, if we are to call the Quartzytes either 

 Llandeilo or Caradoc, the evidence of the fossils is plainly in 

 favour of the former. It is probable enough that the differences 

 which undoubtedly do exist in the fossil associations as compared 

 with those of the tjrpical Silurian areas, are due to the fact 

 that the Cornish area — like that of Brittany, from which the 

 Budleigh-Salterton pebbles have been derived — was more or less 

 isolated. This would account for the fact that the fossils as a 

 whole have a somewhat peculiar fades, and exhibit differences 

 from those of the typical areas, which, though not of specific 

 importance, are yet quite sufficient to account for the great 

 variations existing in the nomenclature adopted by different 

 observers of the brachiopoda.*' 



The 20,000 feet of Lower Silurian Rock — which we certainly 

 have in Cornwall — appears to represent formations which, though 



* These differeuccs will be very evident on comparing the figures 

 given by Murcliisou (" Silima," 5th Ed., 1872), and Davidson {Pal. 

 Soc, 1881). 



