12 Secondary Fossils. 



tile life have been traced back from the Permian to the bot- 

 tom of the Carboniferous deposits, or nearly as far as any 

 land-plants, and farther than the oldest land-shells, yet 

 known. They have been carried down as it were, in six 

 years, through a voluminous series of documents, 15,000 feet 

 or more in thickness ; and we ought therefore by no means 

 to despair of tracing birds or -any other inhabitants of the 

 land to periods as remote. 



Secondary Fossils, 



I will now proceed to consider the bearing of the organic 

 remains of the secondary formations, from the trias to the 

 chalk inclusive, on the doctrine of successive development. 

 Respecting the Invertebrata of this vast period, I need only 

 say, that memorials of all the aquatic tribes are as abundant 

 as we could expect to find those of living invertebrata in the 

 bed of the actual seas. But it is worthy of notice, that the 

 freshwater and terrestrial mollusca are usually, as in older 

 formations, very rare or entirely wanting. No helices or 

 other land-shells have been collected, for example, from the 

 lias, although Mr Brodie in his valuable " History of British 

 Insects" informs us, that in the marl-stones and shales of this 

 age, in Gloucestershire and other parts of the West of Eng- 

 land, there are numerous remains both of insects and plants 

 occasionally mingled with marine shells, sometimes also with 

 freshwater mollusca of the genera Cyclas and Unio. One 

 shale containing Cypris is charged with the wing-cases of 

 Coleoptera, and some nearly entire beetles of which the eyes 

 are preserved. The nervures of the wings of the neuropterous 

 insects are also found in a very perfect state in the same bed. 

 Throughout an extensive district several bands of this lias 

 have been termed insect-limestone, in consequence of the 

 great number of such fossils, no less than 300 specimens of 

 hexapods having been obtained, comprising both wood-eating 

 and herb-devouring beetles of the Linnaean genera Carabus 

 Elater, and others, besides Grasshoppers {Gryllus) and de- 

 tached wings of Dragon-flies and May-flies, or insects refer- 

 able to the Linnaean genera Libellula, Ephemera, Hemerobius, 

 and Panorpa, the whole assemblage belonging to no less than 

 twenty-four families. These have evidently been washed 



