260 THE OLDEST AIR-BREATHERS 



these creatures, found at various times and at various places, 

 are scattered through papers ranging in date from 1844 to 

 1891,^ and are too fragmentary to give complete information 

 respecting the structures of the animals, and their conditions 

 of existence. 



Footprints. 



It has often happened to geologists, as to other explorers of 

 new regions, that footprints on the sand have guided them to 

 the inhabitants of unknown lands, and such footprints, pro- 

 verbially perishable, may be so preserved by being filled up 

 with matter deposited in them as to endure for ever. This we 

 may see to-day in the tracks of sandpipers and marks of rain- 

 drops preserved in the layers of alluvial mud deposited by the 

 tides of the Bay of Fundy, and which, if baked or hardened 

 by pressure, might become imperishable, like the inscriptions 

 of the old Chaldeans on their tablets of baked clay. The 

 first trace ever observed of reptiles in the Carboniferous 

 system consisted of a series of small but well-marked foot- 

 prints found by Sir W. E. Logan, in 1841, in the lower coal 

 measures of Horton Bluff, in Nova Scotia ; and as the authors 

 of most of our general works on geology have hitherto, in so 

 far as I am aware, failed to do justice to this discovery, I shall 

 notice it here in detail. In the year above mentioned. Sir 

 William, then Mr. Logan, examined the coal fields of Penn- 

 sylvania and Nova Scotia, with the view of studying their 

 structure, and extending the application of the discoveries as 

 to beds with roots, or Stigmaria underclays, which he had made 



have been recognised on the continent of Europe, in Great Britain, and in 

 the United States. They belong to a number of distinct types, all, however, 

 being of batrachian affinities. 



^ Papers by Lyell, Owen, and the author, in the Journal of the Geolo- 

 gical Society of London, i. ii. ix. x. xi. xvi. xvii. xviii. ; "Acadian Geology," 

 by the author ; Papers in Trans. Royal Society of London, Am. J I. of 

 Science, and Geological Magazine. 



