ion NEW YOEK STATE MUSEUM 



Cheiracantlius, Cheirolepis, Coccosteus, Dip- 

 lacanthus, Diplopterus, Dipterus, Glvpto- 

 lepis, Osteolepis, and Pterichtliys are especially 

 characteristic. Some of the shales are crowded with the little 

 crustacean Esther ia membranacea. Land plants 

 abound, especially in the higher groups of the flagstones, where 

 forms of Psilophyton, Lepidodendron, Stig- 

 maria, Gala mites and C y c 1 o p t e r i s as well as other 

 genera occur." 



I have found no record of this E s t h e r i a occurring in Brit- 

 ain outside the limits of the sediments of Lake Orcadie. 



Continuing with Geikie's observations, we cite his determina- 

 tion of the period of time covered by the depositions of the Old 

 Red sandstone. 



In Lanarkshire [Lake Caledonia] about 5000 feet above the 

 base of the system a thin band of shale occurs, containing a 

 graptolite, with Spirorbis lewisii and Orthoceras 

 d i m i d i a t u m — undoubtedly Upper Silurian forms. This in- 

 teresting fact serves to indicate that, though geographical 

 changes had elevated the Upper Silurian sea floor partly into 

 land and partly into isolated inland water basins, the sea out- 

 side still contained an Upper Silurian fauna which was ready 

 on any favorable opportunity to reenter the tracts from which 

 it had been excluded. The interval of its reappearance seems 

 to have been very brief however, for the band of shale contain- 

 ing these Upper Silurian marine organisms is only a few inches 

 thick, and the fossils have not been detected on any other hori- 

 zon. With these exceptions the fauna of the formation con- 

 sists entirely of fishes and crustaceans ... 



An interesting fact deserves mention here, as a corollary to 

 what has been stated above regarding the survival for some 

 time of the Upper Silurian fauna outside the area of the British 

 Old Red sandstone lakes. In the upper Old Red sandstone of 

 the basin of the Firth of Clyde, Pterichthys major and 

 Holoptychius occur at the Heads of Ayr, while a band of 

 marine limestone lying in the heart of the red sandstone series 

 in Arran is crowded with ordinary Carboniferous limestone 

 shells, such asProductus gig an tens, P. semiretic- 

 ulatus^ P. punctatus, Chonetes hardrensis, 

 Spirifera lineata, etc. . . . Thus we see that while, 

 on the one hand, the older parts of the lower Old Red sand- 

 stone were coeval with an Upper Silurian fauna which, having 



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