514: MOUNTAIN LIMESTONE. [Oh. XXY. 



had been recognized by the evidence of footprints only. We have 

 still but one species of land-sbell and one centipede. In regard to 

 Archegosaurus, of which there are two species, M. Herman von Meyer 

 informed me some years ago that the remains of more than 228 indi- 

 viduals passed through his hands soon after the true nature of the first 

 specimen was recognized ; and we have seen what great progress has since 

 been made in bringing to light reptilian genera less aquatic in their 

 organization. Nevertheless, the rarity of air-breathers is still a very 

 remarkable fact, when we reflect that our opportunities of examining 

 strata formed in close connection with ancient land exceed in this case 

 all that we enjoy in regard to any other formations, whether primary, 

 secondary, or tertiary. We have ransacked hundreds of soils re- 

 plete with the fossil roots of trees — have dug out hundreds of erect 

 trunks and stumps, which stood in the position in which they grew 

 — have broken up myriads of cubic feet of fuel still retaining its vege- 

 table structure — and, after all, we continue almost as much in the 

 dark respecting the invertebrate air-breathers of this epoch, as if the 

 Coal had been thrown down in mid-ocean. The early date of the car- 

 boniferous strata cannot explain the enigma, because we know that 

 while the land supported a luxuriant vegetation, the contemporaneous 

 seas swarmed with life — with Articulata, Mollusca, Radiata, and 

 Fishes. We must, therefore, collect more facts, if we expect to solve 

 a problem which, in the present state of science, cannot but excite 

 our wonder ; and we must remember how much the conditions of this 

 problem have varied within the last twenty years. We must be con- 

 tent to impute the scantiness of our data and our present perplexity 

 partly to our want of diligence as collectors, and partly to our want 

 of skill as interpreters. We must also confess that our ignorance 

 is great of the laws which govern the fossilization of land-animals, 

 whether of high or low degree. 



CARBONIFEROUS OR MOUNTAIN LIMESTONE. 



It has been already stated (p. 466), that this formation underlies 

 the Coal-Measures in the South of England and Wales, whereas in 

 the North and in Scotland marine limestones alternate with Coal- 

 Measures, or with shale and sandstones, sometimes containing seams 

 of Coal. In its most calcareous form the Mountain Limestone is 

 destitute of land-plants, and is loaded with marine remains — the 

 greater part, indeed, of the rock being made up bodily of corals and 

 crinoids. 



The Corals deserve special notice, as the cup and star corals, which 

 have the most massive and stony skeletons, display peculiarities of 

 structure by which they may be distinguished, as MM. Milne Edwards 

 and Haime first pointed out, from all species found in strata newer 

 than the Permian. There is, in short, an ancient or Palaeozoic, and a 



