496 COAL-FIELDS OF THE UNITED STATES. TCk. XXV. 



CHAPTER XXV. 



carbonifekous group, continued. 



Coal-fields of the United States — Section of the country between the Atlantic and 

 Mississippi — Position of land in the carboniferous period eastward of the Alle- 

 ghanies — Mechanically formed rocks thinning out westward, and limestones 

 thickening — Uniting of many coal-seams into one thick bed — Horizontal coal 

 at Brownsville, Pennsylvania — Vast extent and continuity of single seams of 

 coal — Ancient river-channel in Forest of Dean coal-field — Climate of car- 

 boniferous period — Insects in coal — Rarity of air-breathing animals— Great 

 number of fossil fish — First discovery of the skeletons of fossil reptiles — Foot- 

 prints of reptilians — First land-shell found — Rarity of air-breathers, whether 

 vertebrate or invertebrate, in Coal-measures — Mountain limestone — Its corals and 

 marine shells. 



It was stated in the last chapter that a great uniformity prevails in 

 the fossil plants of the coal-measures of Europe and North America ; 

 and I may add that four-fifths of those collected in Nova Scotia have 

 been identified with European species. Hence the former existence, 

 at the remote period under consideration (the carboniferous), of a 

 continent or 2hain of islands where the Atlantic now rolls its waves 

 seems a fair inference. Nor are there wanting other and independent 

 proofs of such an ancient land situated to the eastward of the present 

 Atlantic coast of North America ; for the geologist deduces the same 

 conclusion from the mineral composition of the carboniferous and 

 some older groups of rocks as they are developed on the eastern 

 flanks of the AUsghanies, contrasted with their character in the low 

 country to the westward of those mountains. 



The annexed diagram (fig. 552) will assist the reader in under- 

 standing the phenomena now alluded to, although I must guard him 

 against supposing that it is a true section. A great number of details 

 have of necessity been omitted, and the scale of heights and horizon- 

 tal distances are unavoidably falsified. 



Starting from the shores of the Atlantic, on the eastern side of the 

 Continent, we first come to a low region (a b), which was called the 

 alluvial plain by the first geographers. It is occupied by tertiary and 

 cretaceous strata, before described (pp. 242, 309, and 338), which are 

 nearly horizontal. The next belt, from b to c, consists of granitic 

 rocks (hypogene), chiefly gneiss and mica-schist, covered occasionally 

 with unconformable red sandstone, No. 4 (New Red or Trias ?), re- 

 markable for its footprints (see p. 454). Sometimes, also, this sand- 



