274 Evolution and Distribution of Fishes 



I say apparent because In collecting fossils from coal pits 

 there Is always great difficulty In accurately determining, 

 to within a few feet or inches, the exact bed where each is 

 obtained; very few Indeed can be obtained in situ, the great- 

 er part are gathered from the spoil-heaps, where accurate 

 reference to any horizon is next to Impossible. A fresh- 

 water bed a few Inches thick would pass unnoticed, and Its 

 fossils be mixed with those from marine beds above or be- 

 low It. Many very thin beds containing fossils peculiar 

 to themselves are known to occur at many geological hori- 

 zons, and as I shall describe hereafter, certain narrow bands 

 containing a typical marine fauna do occur In the Upper 

 Carboniferous strata, only to be recognized as of marine 

 origin by their fossil contents. So that I conceive It to be 

 highly probable that thin freshwater bands exist among 

 the marine beds at the base of the Coal Measures, a series 

 universally recognized as once deposited under changing 

 conditions." 



Quoting from Dr. John Young (202:223) we read 

 "as far as Scotland is concerned I have never observed any 

 commingling of true marine fossils In any of our mussel- 

 band beds. The reptiles, fishes, molluscs, annelids, ostra- 

 cods, and other organisms belong to genera and species 

 that are seldom or never met with in marine limestone 

 strata. This being the case, I believe the opinions formerly 

 entertained, as to the marine origin of the strata of our 

 upper and middle Coal Measures, especially of the bed 

 characterized by Anthracomya was an opinion based on 

 faulty observation, and which will yet be proved to be un- 

 true when the fossils occupying each horizon of strata 

 come to be critically examined. Oscillations of the earth's 

 crust, may bring strata, which have been deposited under 

 either lacustrine or estuarine conditions. Into very close 

 contact with those of true oceanic deposits, and this may 

 be repeated again and again In the same series of beds. 

 It becomes therefore the work of the palaeontologist 

 to say which of the organisms found In this commingling 

 of beds properly belong to the sea, and which to lakes and 

 rivers." 



