50 REPORT — 1865. 



On the Fossil Plants of the Post-Pliocene Deposits of Canada in Connexion 

 with the Climate of the Period, and the Formation of Boulder Clay. By 

 Principal J. W. Dawson, LL.D., F.B.S. 



The author said the leading deposits are, in descending order, the Saxicava-sand 

 and Leda-clay, and the Boulder-clay ; but the latter, though locally under the Leda- 

 elay, is of various ages. Instances were referred to of boulder deposits older than 

 the Leda-clay, contemporaneous with this and the Saxicava-sand, and also later than 

 either. Many arguments were adduced to show that in Canada the striation of 

 both surfaces and the deposit of Boulder-clay had taken place under the influence 

 of ice drifted by ocean currents, and that there was no evidence of any period when 

 the continent was covered with glaciers, though these may have existed on parts 

 of the land remaining above water in the period of depression. It was shown that 

 the driftage had been from the north-east, or against the slope of the country ; 

 that the materials of the deposit were of such a character as to prove that they could 

 not have constituted subaerial moraines, and that marine fossils occur in some parts 

 of the Boulder-clay. The paper next referred to the action of icebergs in the Straits 

 of Belleisle, and on the coast of Newfoundland, showing that their vast numbers 

 and great size, together with their movement and frequent grounding, must enable 

 them to produce great mechanical effects. The author quoted evidence to show 

 that more than four hundred large bergs are sometimes acting at one time in the 

 Straits of Belleisle, and showed that during the Post -pliocene submergence the in- 

 fluence of icebergs and the Arctic current must have been exercised in a similar 

 manner over the whole of the St. Laurence Valley. The last point discussed was 

 the nature of the flora of the Post-pliocene in Canada. The species of plants 

 found in these deposits were noticed, and their present range stated, from which it 

 appeared that they constitute a somewhat aerial but not Arctic assemblage, and 

 would indicate no greater refrigeration than that which would be due to the actual 

 subsidence proved to have occurred. This inference would also correspond with 

 the evidence of the animal remains and with the effects attributed to the Arctic 

 cm-rent, bearing its annual burden of ice over the submerged land. 



The Succession of Palaeozoic Floras in North America. 



By Principal J. W. Dawson, LL.D., F.B.S. 



The Palaeozoic formations of Eastern North America may be grouped in four 



great ages, each characterized by a distinct fauna and flora, and a corresponding 



series of physical conditions. These are the Lower Silurian, the Upper Silurian, 



the Devonian, and the Carboniferous, each of which constitutes a great cycle of 



Ealneozoic time. The rocks, supposed to be Cambrian, are imperfectly known, and 

 ave afforded no fossils. The Permian group has not been recognized. 



1. The Carboniferous flora may be arranged in three subordinate groups. 

 (1) That of the Upper Coal formation, consisting of a few of the more widely 

 distributed species of the Middle Coal formation. (2) That of the Middle Coal 

 formation, the head-quarters of the peculiar Carboniferous flora and of the pro- 

 ductive beds of coal. (3) That of the Lower Carboniferous Coal-measures, con- 

 sisting of a few peculiar species, several of which are not found in the overlying 

 parts of the system. These plants have been recently recognized at this period in 

 Eastern America, and a similar group seems to have existed at the same time in 

 Great Britain. The whole coal-flora in British North America may be estimated 

 at about 150 good species, of which the greater number are common to America 

 and Europe. 



2. The Devonian rocks in Eastern America have afforded eighty-one species of 

 land plants, of which only .about ten are common to this and the Carboniferous 

 period. They occur principally in the Upper. Devonian, but some extend to the 

 bottom of the system. Though fewer in species, the Devonian flora is not lower 

 in grade than that of the Carboniferous period. The earliest known species are 

 allied to Lyeopodiacea. The Devonian flora has been recognized in Pennsylvania, 

 New York, Ohio, Canada, Maine, and New Brunswick. The number of species 

 common to the Devonian of Europe and America is not so great as in the case of 

 the Carboniferous. 



