PHYSICAL AND CLIMATAL CONDITIONS. 139 



abundant on the coasts of Prince Edward island and 

 northern New Brunswick, the Quahog or Wampum shell, 

 the Petricola pholadiformis, which, along with Zirfea 

 crispata, burrows everywhere in the soft sandstones and 

 shales ; the beautiful Modiola plicatula, forming dense 

 mussel-banks in the sheltered coves and estuaries; 

 Cytherea (Oallista) convexa ; Cochlodesma, leana and Cum- 

 mingia tellinoides ; Crepidulafornicata,ihQ slipper-limpet, 

 and its variety unguiformis, swarming especially in the 

 oyster beds ; Nassa obsoleta and Buccinum cinereum, with 

 many others of similar southern distribution. Nor is 

 the fauna so very meagre as might be supposed. My own 

 collections from Northumberland strait include about 

 fifty species of mollusks, and some not possessed by me 

 have been found by Mr. Whiteaves. Some of these, it is 

 true, are northern forms, but the majority are of New 

 England species. 



The causes of this exceptional condition of things in 

 the Acadian bay carry us far back in geological time. The 

 area now constituting the gulf of St. Lawrence seems to 

 have been exempt from the great movements of plication 

 arid elevation which produced the hilly and metamorphic 

 ridges of the east coast of America. These all die out 

 and disappear as they approach its southern shore. The 

 tranquil and gradual passage from the lower to the upper 

 Silurian ascertained by Billings in the rocks of Anticosti, 

 and unique in North America, furnishes an excellent 

 illustration of this. In the Carboniferous period the gulf 

 of St. Lawrence was a sea area as now, but with wider 

 limits, and at that time its southern part was much filled 

 up with sandy and muddy detritus, and its margins were 

 invaded by beds and dykes of trappean rocks. In the 

 Triassic age the red sandstones of that period were 



