Physical Geography. 115 



distinct in space, if not in time, from the marine Devonian 

 strata, for in most books both are generally included 

 under the term Devonian, and the ordinary reader 

 makes no distinction between them. There is, however, 

 this marked distinction, that one is of marine and the 

 other of fresh- water origin, and therefore that the latter 

 belongs to a broad Continental area, outside the shores of 

 which our British Devonian beds were deposited, while 

 in other areas, such as part of Russia, the intermingling 

 of fresh-water and marine inter stratifications seems to 

 imply a set of estuarine conditions. That our Old Red 

 Sandstone, to the very top, was of fresh-water origin is 

 evident, not only by the presence of special genera of 

 fish, but also in the rocks of Dura Den, of a fresh- water 

 shell, Anodonta Jukesii, and of ferns, Adiantites Hi- 

 bernicus and Cyclopteris, also Lepidodendron, &c. 

 The shell proves fresh water, and the plants the vicinity 

 of land. See Fig. 25, p. 101. 



When all the foregoing statements are fairly con- 

 sidered, it seems to me that we obtain sufficient mate- 

 rial from which to form a conception of the physical 

 geography of our area during the deposition of the Old 

 Red Sandstone ; as follows : 



In a mountainous region of which the Scandinavian 

 chain formed part, the lakes of the Old Red Sandstone 

 epoch lay ; for patches of these strata opposite Scotland, 

 and bordering the sea, lie on the Norwegian coast. 

 What was the extent of the Great Lake in which the 

 central Scottish strata were deposited I am unable to say, 

 for they strike out to sea in the Firth of Clyde on the 

 west and to the North Sea on the east coast, forming a 

 stretch of country 100 miles in length by about 60 in 

 breadth. Whether or not, the Old Red Sandstone of 



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