550 Geological Society: Anniversary Address, 1843. 
larger than those which now prevail, has recently been sustained 
by the Rey. Mr. Schooleraft, an American geographer, in a memoir 
which he read before the Geological Section of the British As- 
sociation at Manchester. This author, who has passed nearly 
twenty years of his life in their vicinity, believes that the former 
great lakes have been lowered by ancient dislocations. As examples 
of the bottoms and edges of these former sheets of water, he adduces 
large belts and tracts of sandy plains, which, from their scanty vege- 
tation and undulated surfaces, have all the appearance of recent desic- 
cation; and as proofs of the water having stood at various levels, he 
states, that it has left marks of erosion on the mural faces of the 
harder rocks. But the most original part of this communication, and 
which may indeed serve to explain the origin of some of the ridges 
respecting whose origin Mr. Lyell differs from the writers before 
alluded to, is the actual production of sand-storms by causes associ- 
ated with these lakes. Indicating some of the most extensive energies 
of this nature proceeding from Lake Superior, and the powerful 
action of storms upon sandstone and grauwacke rocks, Mr. School- 
craft is of opinion, that by a union of powerful currents and furi- 
ous gales, dunes have been formed which rise to 300 feet above 
the water. The sand, being first worked up in great bars, has since 
been transported by the wind over wide tracts, which are thus ren- 
dered sterile; stagnant pools are formed in adjacent depressions, 
once highly preductive, and prostrated and buried trees are there 
associated with freshwater shells ; and thus by actual causes, forma- 
tions of considerable thickness are accumulated. Geologists have 
long been aware, that wind has been an agent in heaping up some 
of the deposits whose origin they endeavour to explain, and very 
striking examples of this operation were adduced by Lieut. (now 
Capt.) Nelson, R.E., in his account of the modern shelly and sandy 
limestone of the Bermudas. As no one, indeed, has a better acquaint- 
ance with this class of phenomena than Mr. Lyell, it is enough for me 
to have attracted his notice to the vivid descriptions of Mr. School- 
eraft, which may, I think, aid in explaining some of the superficial 
appearances in the lake country of North America. 
Let us return, however, to the memoirs of Mr. Lyell. Reviewing 
the series of changes which have taken place in the Canadian and 
Lake region, Mr. Lyell conceives, that after an early period of emer- 
gence, during which lines of escarpment and valleys of denudation 
were excavated in solid rocks, the surface of the country was 
submerged, and the cavities filled with the marine boulder forma- 
tion ; and that during the last elevation of the land, the parallel sand 
ridges were produced, the boulder formation partially denuded, and 
the different lakes probably formed in succession, leaving a partial 
sea channel, which, contracting first into an estuary, was eventually 
converted into the river Niagara. Reaching this point in his order of 
events, our author succeeds most happily in developing his views 
concerning the retrocession of the falls of this river ; bringing for- 
ward arguments to show that during the re-emergence of the land 
from the sea, a succession of falls must first have been established 
