THE OLDEST AIR-BREATHERS 297 



worm shell (Spirorbis) found with them, are not necessarily 

 marine, though some of them belonged probably to brackish 

 water, and they have not yet been found in those carboniferous 

 beds deposited in the open sea. There is thus in the whole 

 thickness of the middle coal measures of Nova Scotia a 

 remarkable absence at least of open sea animals ; and if, as is 

 quite probable, the sea inundated at intervals the areas of coal 

 accumulation, the waters must have been shallow, and to a 

 great extent land-locked, so that brackish-water rather than 

 marine animals inhabited them. 



On the other hand, there are in these coal measures 

 abundant evidences of land surfaces ; and subaerial decay of 

 vegetable matter in large quantity is proved by the occurrence 

 of the mineral charcoal of the coal itself, as I have elsewhere 

 shown. 1 The erect trees which occur at so many levels also 

 imply subaerial decay. A tree imbedded in sediment and 

 remaining under water, could not decay so as to become 

 hollow and deposit the remains of its wood in the state of 

 mineral charcoal within the hollow bark. Yet this is the case 

 with the greater part of the erect Sigillariae which occur at 

 more than twenty levels in the Joggins section. Nor could 

 such hollow trunks become repositories for millipedes, snails 

 and reptiles, if under water. On the other hand, if, as seems 

 necessary to explain the character of the reptiliferous erect 

 trees, these remained dry, or nearly so, in the interior, this 

 would imply not merely a soil out of water, but comparatively 

 well drained ; as would indeed always be the case, when a flat 

 resting on a sandy subsoil was raised several feet above the 

 level of the water. Further, though the peculiar character of 

 the roots of Sigillarm and Calamites may lend some counten- 

 ance to the supposition that they could grow under water, or in 

 water-soaked soils, this will not apply to coniferous trees, to 



1 Journal of Geological Survey ', vol. xv. 



