HOW THE COAL BEDS 



plates of considerable thickness on its head and shoulders 

 (some fine examples are to be seen at the Natural History 

 Museum, Cromwell Road, London), but its tail and middle 

 body were left unprotected. The sharks of to-day had 

 their representatives among the Devonian fishes. Sharks 

 have throughout geological time nearly always been sea- 

 dwellers, though they still occasionally live in fresh water, 

 as in Lake Baikal in Siberia and Lake Nicaragua. It seems 

 clear, however, that in the Devonian period they lived in 

 the open sea. But their remains are found in the Old Red 

 Sandstone, and therefore it is likely that they lived in 

 fresh and brackish waters also. In the same strata as 

 these remarkable fishes there are found some large and 

 peculiar crustaceans, something like our modern king 

 crabs, but reaching the enormous length of six feet. 

 There have also been mussels found and a few water 

 plants, but not many. 



In the Devonian relics the land vegetation has for the 

 first time been fairly well preserved. The huge club 

 mosses made good their tenure on the land ; and along the 

 flats and low-lying lands by the rivers there were dense 

 brakes of reedy calamites and masses of true ferns. The 

 club mosses and the calamites diminished from their giant 

 size eventually, but the ferns went on increasing, and 

 ancestral types of the pines and the yews began to 

 appear. The vegetation of Devonian times was sombre ; 

 there could have been no flowers, and the insects were not 

 of the kind that speed from bloom to bloom. Insects 

 there were, gigantic dragon-flies and insects akin to the 

 many flies that haunt the water ; but the myriad buzz of 



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