ENVIRONMENT OF THE OYSTER 97 



Indian shell heaps and in Pleistocene fossils, as well as in the present dis- 

 tribution of faunas. 



There appears to be an arctic or circum-polar fauna which extends southward to 

 varying distances into the Atlantic and Pacific oceans, permitting certain species to be 

 obtained indifferently off the Alaskan, Labrador, or Scandinavian coasts. Its general 

 southern surface limit is Baffin bay, but it can be traced in deep water into the gulf 

 of St. Lawrence. 



A Syrtensian or intermediate fauna extends from northern Greenland downwards 

 along the Labrador shore, on both sides of Newfoundland, in the northern part of the 

 gulf and estuary of the St. Lawrence, and from the Grand bank off the south of New- 

 foundland westward on all the fishing banks off the Nova Scotia coast to St. George 

 bank and the entrance to the bay of Fundy. 



An Acadian or Nova Scotian fauna occupies the southern and western portions 

 of the gulf, generally delimited from the Syrtensian by a line drawn from cape 

 Gaspe outside of the Magdalen islands to the northern point of Cape Breton, but 

 continuing between Anticosti island and Gaspe peninsula where it mingles with the 

 Syrtensian fauna. Southward it is found in the shallower coastal waters on the south 

 of Newfoundland, Cape Breton, and Nova Scotia, as well as in the bay of Fundy (ex- 

 cepting its deepest parts), whence it continues along the New England coast to cape 

 Cod. 



The natural bounds of the Virginian fauna are cape Cod and cape Hatteras, but 

 it has outlying colonies in the gulf of St. Lawrence, on the southern shore of New- 

 foundland, on Sable island and the coasts of Cape Breton and Nova Scotia, as well as 

 to a slighter extent in the more sheltered of the head waters of the bay of Fundy. It 

 is also represented in Casco and Massachusetts bays leading down to its more natural 

 northern limit. 



The oyster (Ostrea virginiana) belongs to the Virginian fauna, which includes the 

 quahaug {Venus mercenaria) , the ribbed mussel (Modiola plicata), a bar clam (Mactra 

 lateralis), a scallop (Pecten irradians) , and a number of species of smaller Bivalves, 

 such as Teredo dilatata, Cummingia tellinoides, Montacuta elevata, Petricola pholadi- 

 formis, Cytherea convexa, and perhaps others along the Acadian coasts. To it belong 

 also many Gastropods well known on our coasts such as Crepidula fornicata, plana and 

 convexa, Bittium nigrum, and Greenii, Nassa obsoleta, Odostomia bisuturalis, trifida, 

 and seminuda, Astyris lunata, Turbonilla interrupta, Utriculus canaliculars, Bulla 

 solitaria, Buccinum cinereum. In a similar manner there might be added representa- 

 tives from other great phyla beside the Mollusca, but of less interest in the present 

 connection. Some of these species are so constantly associated with the oyster that 

 wherever they are found it is understood that the oyster may be looked for, or has 

 perhaps formerly lived there, or at least that the physical conditions are largely suited 

 to its requirements. 



The Canadian representatives of the Virginian fauna may have wandered north- 

 ward during some warmer period such as that which prevailed in Greenland at the 

 time of its discovery by the Norse sea-rovers in the ninth century. The name Greenland 

 given by one of them, Erik the Red, about 980, commemorates the fact of its hav- 

 ing once possessed a more genial climate. However this may have been, it is evident 

 that for the last few centuries and at the present time, the oyster and other members 

 of the Virginian fauna are being slowly driven southward by aggression of that Arctic 

 climate which has changed the physical conditions of Greenland. 



The explanation of this astonishing climatic change is forthcoming from the facts 

 of geology and physical geography. It has been shown by Gesner, Dawson, Matthew, 

 Hind, Murphy, Chalmers, and others, that the Atlantic sea-board of this continent 

 is undergoing a slow but gradual subsidence, which has amounted in places to 

 as much as eighty feet, while on the other side of the ocean, as is also well known, the 

 coast of Scandinavia and adjacent countries is slowly rising. Such geological changes 

 of level, affecting not only the opposite continents but extending also to the ocean 

 bed, has, according to Verrill, thrown the southwardly flowing cold Arctic Current 

 closer to our shores, while the warm Gulf Stream from the south, due to its outside 

 situation and the configuration of the land, only proceeds as far as to the south of 

 Newfoundland before it is deflected across towards the coast of Norway. 



