Science, Geology and Physics 



GILBERT, Grove Karl. The history of the Niagara river. (Ann. 1889 

 rep'ts of the com'rs of the state reserv. at Niagara. Albany: 1 890. Gilbert 

 6:61-84.) 



The substance of a lecture read to the American Association for the 

 Advancement of Science at its Toronto meeting, August, 1 889, and deals 

 with the origin of the river and its mode of recession, together with a list 

 of the factors entering into and some of the questions to be answered 

 before any solution of the time problem can be regarded as satisfactory. 



The difference between the two processes is of great impor- 

 tance in the present connection, because the two rates of erosion 

 are very different. 



I am fully aware that this sketch of the cataract's work is not 

 a satisfactory explanation of the mode of recession, but it yet 

 serves a present purpose, for it renders it possible to point out 

 that the rate of recession is affected by certain factors which may 

 have varied during the earlier history of the river. We see that 

 the process of recession is concerned with a heavy bed of hard 

 rock above, with beds of softer rock beneath, with the force of 

 falling water, and possibly, also, with the solvent power of the 

 water. 



Concerning each of these factors a number of pertinent ques- 

 tions may be asked, questions that should certainly be considered, 

 whether they are answered or not, before any solution of the 

 time problem is regarded as satisfactory. To illustrate their per- 

 tinence, a few will be propounded. 



Question 1. Does the limestone vary in constitution in dif- 

 ferent parts of the gorge? If its texture or its system of cracks 

 and joints varies, the process of recession may vary in consequence. 



Question 2. How does the limestone bed vary in thickness in 

 different parts of the gorge? This question is easily answered, 

 for at all points it is well exposed for measurement. 



Question 3. How is the thickness of the limestone related to 

 the rate of recession? This is more difficult. The debris from 

 a very thick bed of limestone would oppose great resistance to 

 the cataract and check its work. The debris from a very thin 

 bed would afford small and inefficient pestles for pot-hole action, 



579 



