No. 5.] SPENCER — SURFACE GEOLOGY. 291 



lower outlets to the lacustrine sea, but also raised many of the 

 lower rido'es to the south by an ice barrier sufficient to prevent 

 the overflow of its waters. As remarked by Prof. Dana, no 

 moraines bear evidence of such a dam at 1000 feet above the sea. 

 In the Province of Ontario the stratified drift in very many 

 places is at a much higher level than long stretches of the barrier 

 ranges to the south. Moreover, at the time when part of these 

 stratified deposits were being produced the sea contained little or 

 DO floating ice wherewith to close the outlets, much less to in- 

 crease heights of the barriers. 



Consideration of Changes of Level and Deposit of Boulder 

 and other Clays. — According to the glacial theory the continent 

 stood at a much higher elevation in the ice age than at the present 

 time, yet it does not demand any very great changes of level. So 

 also in the above remarks, the subject of local oscillations has not 

 been an element of consideration, yet great changes of level did 

 take place. The marine boulder drift of the St. Lawrence valley, 

 containing Arctic shells, reaches an elevation of over 500 feet, 

 irrespective of higher and more modern terraces. Also the coast 

 of Labrador has been known to have risen to areat heights since 

 the ice age. Prof. Dana remarks that the continent was more 

 elevated to the northward than the southward. 



During the great accumulation of ice along the mountains of 

 Labrador, Quebec, New England, New York, etc., and in f^ict 

 around the north Atlantic, there would have been a relative sink- 

 ing of the continent arisinii" from the change of the centre of 

 o-ravity of the earth. The subsidence would besfin along the 

 x\tlantic coast and extend westward. We know that the large 

 deposits of Boulder clay in the St. Lawrence valley are marine 

 and deposited beneath water. However, on moving up the St. Law- 

 rence valley the evidences of the marine character gradually disap- 

 pear as the Arctic shells cannot be traced to the western deposits. 

 Nor do any of the marine Port Pliocene deposits pass westward of 

 the east end of the valley of Lake Ontario (whose elevation is 247 

 feet above mean tide). The unimportance of the Boulder clay 

 farther west in Ontario, or more frequently its entire absence, 

 with Erie stratified clay containing a few boulders, especially near 

 its base, resting on striated rocks, points to tlie fact that the ice 

 age and the continental subsidence began earlier to the north- 

 ea>;tward than it began in the valley of Lake Ontario and the 

 region to the west of it. This being the case, we have an explan- 



