172 POPULAR SCIENCE MONTHLY. 



agara to tlie Mississippi was completed, the upper lakes were 

 rapidly lowered, and this re-established the life of the Niagara 

 for some time longer. Upon the basis of calculations made it 

 would appear that the change of outlet for the upper lakes from 

 the Niagara to the Mississippi will not be more than another five 

 thousand years hence — to us living a matter of indifference, but 

 only showing how the present days are simply passing events in 

 the history of the lakes. In the meanwhile the waters of Lake 

 Ontario will more and more flood the head of its basin. However, 

 the end of the lakes is so far removed in geological time that, until 

 such great changes in the configuration of the land shall have ob- 

 tained of which we have no prophetic vision, the lakes will con- 

 tinue to exist. 



Age of the Great Lakes. — When the rate of movement of 

 the earth's crust, as determined in the history of Niagara Falls, is 

 applied to the deserted strands of Warren Water and its success- 

 sors, it is estimated that since the commencement of the Warren 

 epoch fifty thousand or sixty thousand years have elapsed. This 

 estimate, although based upon the most analytical knowledge ob- 

 tainable, can, after all, be regarded as only approximate. The 

 time ratio tells us that the lakes are still youthful ; although 

 in terms of solar years very old, yet perhaps not older than the 

 human race. 



The vicissitudes between the end of the ice age proper and the 

 birth of Warren Water are too little known to enter into any pro- 

 portional division of time, except that the ice age culminated prior 

 to or at the date of the closing of the old valleys with drift. 



The Great Lakes are the most striking feature of the eastern 

 part of the continent, yet what we know of their history has been 

 mostly discovered within the last few years. In this sketch only 

 some of the more important and generalized results have been 

 given. Many of the observations are beyond doubt, but there is 

 plenty of room for students to add to our knowledge and correct 

 our imperfect work. While the history of the lakes can be told 

 with considerable .certainty, the attempt at computing their age 

 in terms of solar years has the same fascination, although not so 

 extravagant, as the speculations concerning the antiquity of the 

 earth itself, as the former question probably comes within the 

 human period. 



Harvard College Observatory publishes a list of fourteen new variable 

 stars of long period, in addition to those previously announced, which have 

 been discovered by Mrs. Fleming from the examination of Henry Draper 

 memorial photographs. The spectrum of one of these stars is of the fourth 

 type, while all the otlier stars have spectra of the third type, with the hydro- 

 gen lines also bright. 



