SHIP WORM ON ATLANTIC COAST 101 



SESSIONAL PAPER No. 38a 



reason for this isolation becomes apparent on examination of a bathymetric chart 

 of the waters of the Maritime Provinces. The whole of Prince Edward island and 

 ISTorthumberland strait lie inside the 20-fathom line, and much of the broad strait has 

 a depth of 10 fathoms or less. On the southeastern coast of Nova Scotia, however, the 

 20-fathom line frequently approaches to within one-half mile of the coast, and there 

 is everywhere a narrow zone of shoal water inside the 100-fathom zone which renders it 

 colder than the broad shallow warm waters of Northumberland strait. It illustrates 

 well the fact that a zone of shallow water if sufficiently close to and unprotected from 

 deep waters may serve as a faunal barrier as effectively as a land barrier. This 

 example of an isolated colony of the northern New England shallow zone marine 

 fauna surrounded by a sub-boreal fauna is worthy of the attention of paleontologists 

 who are prone to predict land barriers as offering the only possible explanation of 

 faunal differences similar to those described above. 



FORMER DISTRIBUTION OF THE XORTHUMBEHLAND FAUNA. 



There are several bits of evidence which seem to indicate that the present isola- 

 tion and limited distribution of the colony of comparatively warm- water mollusca 

 now living in the Northumberland strait with which 2\ navalis is associated is of 

 recent origin. Ostrea virginica, the most strikingly southern type of this assemblage, 

 apears to have extended as far westward as Montreal at one time during the Pleisto- 

 cene. Several years ago Sir William Dawson wrote : " I have picked up a loose speci- 

 men at Saco which has the appearance of being a fossil specimen from the Leda clay, 

 and Mr. Paisley has sent me specimens from Chaleur bay which are said to have come 

 from Pleistocene beds 16 feet from the surface." ^ More recently Edward Ardley^ 

 has reported finding Ostrea near ]\Iontrpal, 9 feet below the surface, associated with 

 Mya truncata, Maconia calcarea, Astarte, Laurentiana, and Saxicava rugosa. At Cole 

 Harbour on the east coast of Nova Scotia the flukes of anchors bring up numerous 

 dead oyster shells, where the living oyster is unknown.^ 



On the east coast of Nova Scotia, Mr. W. J. Wintemburg of the section of Archae- 

 ology of the Geological Survey, has found in an old Indian shell heap on Mahone 

 bay, 40 miles southwest of Halifax, shells of Ostrea virginica and Venus mercenaria. 

 Neither shell is known south-west of Halifax, on the east coast of Nova Scotia at 

 present, but their discovery in the shell heap appears to indicate that they lived in the 

 bay when the shell heap materials were accumulating. 



It may be suggested tentatively that, the beds containing 0. virginica at IMont- 

 real are synchronous in time with the Don River interglacial beds at Toronto. It 

 is probable that the milder climatic conditions which prevailed during the early part 

 of the Don River interval'* rendered the temperature of the Atlantic coastal waters of 

 the Maritime Provinces sufficiently mild to give the oyster and its congeners con- 

 tinuous distribution from southern New England to the gulf of St. Lawrence. 



1 Dawson, J. W. Ice Age in Canada, 1893, p. 243. 



- Ardley, Edward. " The Occurrence of Ostrea in the Pleistocene Deposits of the Vicinity 

 of Montreal." Ottawa Naturalist, Vol. 26, 1912, p. 67. 



aProc. and Trans. N.S., Inst. Nat. Sci. Vol. I, 1863, p. 98. 



i A. P. Coleman, Int. Cong. Geol., Guide Book, No. 6, 1913, pp.15-31. 



