I034 PRINCIPLES OF STRATIGRAPHY 



and the beds of the Old Red Sandstone type of the same countries, 

 show the best preserved representatives, these beds being strictly 

 non-marine deposits. Some of the best preserved specimens of 

 Bothryolepis are from the fresh water (river, flood-plain and delta) 

 deposits, which constitute the Gaspe sandstone of eastern Canada. 



The Upper Siluric bone-bed (Ludlow) of England also fur- 

 nishes these remains, and this deposit may have been formed in 

 an estuary, or an enclosed basin near the sea. A few fragmentary 

 remains have been obtained from marine Siluric and Devonic strata, 

 but these, like the similar occurrences of eurypterids, are not satis- 

 factory evidence of the marine character of these fishes. In Penn- 

 sylvania, remains occur in sandstone beds, most probably of river 

 origin, belonging in the Upper Siluric (Monroan) horizon. 



Pisces. The earliest true fish appear in the Siluric, but are 

 more typical of the Devonic. Here the Arthrodires were espe- 

 cially abundant, many of them still inhabiting the rivers of the 

 continent. They began to migrate into the sea, however, judging 

 from the more numerous remains found in open sea deposits, such 

 as the Onondaga limestone. The abundant fish fauna of the Upper 

 Devonic shales of Ohio is associated with tree trunks, spores of 

 land plants, etc., in sediments suggesting a river delta rather than 

 open sea. These Tapper Devonic fish did, however, live in the seas 

 of that time as well, for their remains are also found in undoubted 

 marine strata. The Cyclostomi (or Lampreys) seem to be first 

 represented b} the remarkable Palaeospondylus of the Old Red 

 Sandstone of Caithness, Scotland. The Elasmobranchs, or sharks, 

 also lived in the rivers of Old Red Sandstone time, and their re- 

 mains are found in the semi-terrestrial deposits of the Upper Siluric 

 in Europe and America. These fish, however, entered the sea in 

 Devonic, if not in Siluric. time, and thereafter became chiefly ma- 

 rine organisms, continuing so down to the present time. 



The living ganoids either inhabit fresh water rivers exclusively, 

 or, as in the case of the sturgeons, enter the rivers from the sea. 

 In Pala?ozoic and Mesozoic time they were marine and fluviatile. 

 The living Dipnoi inhabit the tropical swamps of South America 

 ( Lepidosiren) and of Africa (Protopterus) and also the rivers of 

 Queensland (Ceratodus). Ceratodus also occurs in the Bunter 

 Sandstein of Wiirttcmberg, the Keuper of Austria, the Stonesfield 

 slates of England, and the fresh water Jurassic of Colorado. It 

 also occurs in the Kota-Maleri beds of India and in the Karoo 

 formation of South Africa. All of these formations represent river 

 deposits. With few exceptions the other Dipnoans (Ctenodipterini ) 

 also occur in fresh water (chiefly river) deposits, such as the Old 



