ANCIENT WATER LEVELS OF CHAM PLAIN— HUDSON VALLEYS 237 



to 1904 there appears to have been on the whole no permanent 

 change of level. At the international boundary the rate must 

 lie somewhere between 2 feet and 5 feet a century. On the 

 Swedish coast elevation appears to be taking place at a rate 

 of from 2 to 3 feet a century. Thus a rate of change of 

 from 2 to 3 feet appears admissible for certain places on 

 the earth's surface. Assuming that there has been constant up- 

 lift at Mt Royal, and that the rate has been that locally ascer- 

 tained in the case of the Baltic coast and placing this at its maxi- 

 mum of 3 feet a century, it would have required 18,666 years to 

 raise the highest shell bed on that mountain from sea level to its 

 present hight above the sea. Again, if we assume that the rate of 

 elevation has been faster at Mt Royal but not greater than 3 feet 

 a century at the international boundary, where the upper limit of 

 the Hochelag r an marine invasion now stands at 450 feet, 15.000 

 years would be required to accomplish the result. This method 

 of attacking the problem it will be seen is not likely to give 

 definite results unless the actual rate of vertical movement at the 

 point where the elevation of the ancient water level is taken be 

 known. In this district the data have not been gathered. 



Thanks to Mr Gilbert's studies of the changes of level now 

 taking place in the Great Lake basins the assumption may be made 

 that on one of the radial lines of the apparently dome-shaped 

 uplift which has taken place in this northeastern part of the 

 country the rate of tilting on a south-southwest direction is such 

 as to displace the two ends of a line 100 miles long .42 of a foot 

 in 100 years. The line of water level traceable through Lake 

 Ohamplain and southward through the Hudson exhibits a displace- 

 ment showing uplift on the north and depression on the south 

 such as to make the assumption of a southward tilting in this 

 direction at a rate comparable to that made out for the Great 

 Lakes. Making this assumption with the additional postulate that 

 the present rate has held during the past, the following data lead 

 1o the conclusion stated below. 



At Covey hill on the international boundary the marine limit 

 is 450 feet. Twentv-six miles north a littoral deposit of shells 

 occurs on Mt Royal at the hight of 550 feet. The difference of 

 level today between these two stations is at least 100 feet. 



