1875.] 405 [Dodge. 



may be most profitably directed. Their approximate 1 age is readily 

 indicated. 



The British Lower Cambrian ends with the Tremadoc, which has 

 been synchronized with the Levis division of our Quebec Group. 

 Beneath the Tremadoc are the Lingula Flags, and at their base are 

 the rocks at St. David's in South Wales, the corresponding Bangor 

 group in North Wales, and (equivalent to the lower portion of this 

 Welch section) the Longmynd of Shropshire. Parts of the Lingula 

 Flags are supposed to be on a level with our Calciferous and Pots- 

 dam. The Paradoxides of the slates of this vicinity shows so much 

 of them as can be properly grouped together, to be more nearly 

 synchronous with the Menevian and Longmynd than others of the 

 British horizons. 



It has been long supposed, and the results of recent investigations 

 tend to confirm the belief, that the early faunas of the rocks of North 

 America more nearly resemble the coeval ones of Scandinavia and 

 Great Britain, than do those of continental Europe. Yet it is notice- 

 able that in these earliest yet known, some of the Braintree speci- 

 mens are more closely related to Paradoxides spinosus of Bohemia 

 than to any of the Menevian species of Great Britain. It is to be 

 hoped that a new State Geological Survey may soon give us more 

 adequate means of studying the parallelism of our rocks with for- 

 eign ones, and the relations of their respective faunas. 



The last quarter of a century has done but little in this direction. 

 The great trilobite of Braintree, described in 1834, was first discov- 

 ered in place at Hay ward's Creek in 1850 or 1851, but during all the 

 years which have since elapsed, no other locality has been made 

 known, and but one or two species seem to have been recognized 

 from that. This Paradoxides was a better beginning than the worm 

 burrows and few obscure remains found in most localities, inasmuch 

 as it represents, so far as is yet known, the highest existing type of 

 life of that period, as well as because trilobites seem to give the 

 safest test of the age of the strata where they occur. But while it 

 stands almost alone to represent our rocks, the Menevian of South 

 Wales had afforded in 1872, fifty-two distinct species belonging to 

 twenty-two genera ; of which, ten genera, including thirty-one species, 



1 It has been remarked that as contemporaneous faunas and floras of different 

 regions differ widely, so similarity of fossils does not necessarily indicate their ex- 

 istence at the same period. Mr. Hicks has remarked that corresponding fossils are 

 found higher in America than in Europe, instancing Olenus, Olenellus, and Dikel. 

 locephalus. (Quart. Journ. Geol. Soc. Lond., vol. xxvii, p. 395.) 



