Science, Geology and Physics 



than 400,000 tons. If the additional weight and velocity, 1805 

 gained by a fall of 1 58 feet, be added, the weight of these Su,cIlff 

 prodigious columns of water would exceed three millions of tons. 

 Such an enormous specific gravity falling at once into the gulph 

 below, may bring the accounts of the Falls being heard, under 

 favourable circumstances, at the distance of 40 or 50 miles, within 

 the limits of credibility. 



1809 

 MiTCHILL, SAMUEL L. A summary of remarks made on the Falls 1809 

 of Niagara, by the Hon. Samuel L. Mitchill, as gathered from his con- ' c 

 versations and display of mineral specimens. (The Portfolio, Sept. 1 809. 

 2:231-237.) 



On exploring the strata laid bare by the cataract, their argil- 

 laceous, calcareous and silicious character immediately struck 

 him. He was careful to bring away specimens of each; and 

 these at all times and distances enable him to substantiate his 

 own description of the grand falls. 



The inferior layers of earthy matter at the falls are composed 

 of slate, or shistus. This is very friable, and cracked into num- 

 berless pieces. It has so little cohesion that the fragments can 

 be easily picked out by the fingers. It is constantly dropping 

 off or wearing away. Its fallen portions constitute a part of the 

 loose gravel through which the traveller labours beneath. This 

 argillaceous matter yields to mechanical and chymical agency 

 more readily than the harder strata which it supports. It there- 

 fore undergoes excavation, while the superior and firmer strata 

 of limestone project and overhang until they break off by their 

 own weight. Owing to this abrasion or decay of the brittle 

 shistus, the calcareous rocks above jut far beyond their present 

 base, and threaten him who takes shelter below them. Masses 

 of various sizes, from small stones to rocks of many tons weight 

 have fallen from the summit thus undermined, and now occupy 

 the space at its foot. As the excavating or undermining process 

 goes on, other pieces will be detached, and the chasm be pro- 

 portionally enlarged. . . . 



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