93 



(4) In the later stage represented by the Grande Greve 

 limestones the northern passage became broadened while 

 the Dalhousie channel became extinct. In addition to 

 these open passages from the interior outward were others 

 of Devonian date further south, and the relations of these 

 sea ways have been discussed by Clarke (11, p. 153-162.). 



5) The Gaspe sandstones indicate a general breaking 

 down of the barriers of the northern channel which per- 

 mitted a later (lower or middle) Devonian invasion of 

 species from the interior, while the Grande Greve fauna still 

 persisted. Flood and barachois conditions governed the 

 early deposition of these sandstones but encroaching 

 elevation eventually changed the middle and later Devonian 

 conditions to those of a rias coast not unlike that of the 

 present. 



THE ORIGIN OF THE GULF OF ST. LAWRENCE. 



The hydrographic charts of the Gulf indicate very clearly 

 that the course of the ancient St. Lawrence river was from 

 its present mouth southeast, far to the east of Gaspe, east 

 of the Magdalen islands, and thence outward to the Atlantic 

 by the passage between Cape Breton island on the west and 

 Newfoundland on the east (Cabot strait). The St. 

 Lawrence river is a very ancient waterway and takes its 

 date from at least as early as the time of the marine 

 (Levis) channel of the early Ordovician, a passageway 

 which led from Atlantic waters into the Appalachian gulf 

 of the interior of the continent. Fixity was given to this 

 waterway by the long subsequent faulting of the Palaeozoic 

 rocks against the crystalline Labrador shield at the north, 

 and ever since this factor became efficient the passage has 

 been now and again a salt-water channel and a fresh-water 

 drainage way. That part of the river channel now sub- 

 merged beneath the Gulf waters is not the oldest portion 

 but a later part of the river, where the valley was cut out 

 through marine rocks which had been deposited over the 

 bed of the Gulf when that was open ocean. 



The orogenic axes of Appalachian disturbance through 

 the Gulf region are twofold: that at the south, passing 

 through Nova Scotia and on into Newfoundland keeping a 

 N.E.-S.W. trend without change of direction; that at the 



