1865.] DAWSON — POST-PLIOCENE DEPOSITS. 83 



in connection with it I would desire to make some general 

 remarks on the features of these interesting deposits. 



We have here an indubitable instance of a marine boulder-clay. 

 I have observed fossiliferous boulder-clays at Murray Bay, St. 

 Nicholas, and Cape Elizabeth, but the example afforded at Cacouna 

 and its vicinity is more clear and instructive ; and there is also 

 evidence that the surface under the boulder-clay is polished and 

 striated, the direction of the striae being north-east and south-west, 

 or that of the St. Lawrence valley.* 



The Cacouna boulder-clay is a deep-water deposit. Its most 

 abundant shells are Leda truncata, Nucula tenuis, and Tellina 

 proxima, and these are imbedded in the clay with the valves 

 closed, and in as perfect condition as if the animals still inhabited 

 them. At the time when they lived, the Cacouna ridges must 

 have been reefs in a deep sea. Even Mount Pilote has huge 

 Laurentian boulders high up on its sides, in evidence of this. The 

 shales of the Quebec group rocks were being wasted by the waves 

 and currents; and while there is evidence that much of the fine 

 mud worn from them was drifted far to the south-west to form the 

 clays of the Canadian plains, other portions were deposited between 

 the ridges, along with boulders dropped from the ice which drifted 

 from the Laurentian shore to the north. The process was slow 

 and quiet ; so much so that in its later stages many of the boulders 

 became encrusted with the calcareous cells of marine animals 

 before they became buried in the clay. No other explanation can, 

 I believe, be given of this deposit ; and it presents a clear and 

 convincing illustration, applicable to wide areas in Eastern America, 

 of the mode of deposit of the boulder-clay. 



A similar process, though probably on a much smaller scale, is 

 now going on in the Gulf. . Admiral Bayfield has well illustrated 

 the fact that the ice now raises, and drops in new places, multi- 

 tudes of boulders, and I have noticed the frequent occurrence of 

 this at present on the coast of Nova Scotia. At Cacouna itself, 

 there is, on some parts of the shore, a band of large Laurentian 

 boulders between half tide and low-water mark, which are moved 

 more or less by the ice every winter, so that the tracks cleared by 

 the people for launching their boats and building their fishing- 

 wears, are in a few years filled up. Wherever such boulders are 

 dropped on banks of clay in process of accumulation, a species of 



* South 55° west mag., near Cacouna. 



