142 Niagara. (April, 
Dana, in an excellent paper on the Glacial Era in New 
England, has ably argued this question, and has shown the 
enormous power that moving ice, 6000 feet thick, with a 
pressure of at least 300,000 pounds to the square foot, would 
have in abrading the rock surfaces below it, and carrying 
forward in its lower part the loose material it had broken 
off or caught up from the rocks below, and how the whole 
of this would be deposited at the melting of the ice.* It 
would greatly conduce to clear descriptions of glacial phe- 
nomena, if the old term ‘‘ till”” were confined to this deposit. 
It is the “ Erie clay”. of Dr. Newberry,: the’ Mower 
Boulder clay” of Wood, the ‘‘ grund morane”’ and the 
“moraine profonde”’ of others. ‘‘Erie clay” is a local 
name, and includes stratified beds of a different origin. 
‘Boulder clay” is often a misnomer, as frequently this 
clay contains no boulders. ‘‘ Grund morane” and ‘‘ moraine 
profonde”’ indicate a particular mode of origin, which, 
though probably correct, is still theoretical. ‘‘ Till” is an 
old English word, long applied to this deposit, and may be 
used by every one, whatever theory of origin they may 
favour. I suggest, therefore, that it should be confined to 
designate the unstratified clay with angular blocks, gene- 
rally of local origin, that lies at the bottom of all the glacial 
beds, and that the term ‘‘ boulder clay” should be applied to 
the higher beds, which show the action of water as well as of 
ice. The term “drift”? might be applied to any glacial 
deposit the nature and origin of which is doubtful, in the 
same way as the name ‘‘ trap” is used for many igneous 
rocks of unascertained composition. 
The preservation in the St. Lawrence valley, and in the 
Great Lake district, of beds of loose laminated sands and 
clays lying below the till is due, as has been shown by Dr. 
Newberry, to the fact, that the ice was rising against the 
slope of the land. It had, in consequence, little erosive 
power, but advanced principally by the slipping of the 
higher portions of the ice over the lower. When it topped 
the southern water-shed of the valley of the St. Lawrence, 
its action produced a different set of phenomena, for its 
motion was down the slope of the land, and its erosive 
power was vastly increased. With this subject I shall not 
here deal, nor shall I attempt to trace the limits of the ice 
in its greatest extension, as that would lead me into a dis- 
sertation on the whole of the glacial period in North 
America, far beyond the scope of this paper. 
* American Journal of Science and Arts, vol. v., March, 1873. 
