150 POPULAR SCIENCE MONTHLY. 



eiglity-eight feet — that is, the upper stratum of hard rock on the 

 east side of the gorge had retreated that distance, through the action 

 of atmospheric agencies, since the formation of the gorge first began. 

 The accompanying photogravures and diagram will present the facts 

 at a glance. The total work of enlargement on the east side of the 

 gorge has been the removal of an inverted triangular section of the 

 rock strata three hundred and forty feet high and three hundred and 

 eighty-eight feet base, which would be the same as a rectangular 

 section of one hundred and ninety-four feet base. From this one 

 can readily see that if the average erosion has been at the rate of 

 one quarter of an inch per annum, the whole amount would have 

 fallen down in less than ten thousand years; while if the time is 

 lengthened, as some would have it, to forty thousand years, the rate 

 would be reduced to one sixteenth of an inch per year. 



Fortunately, the construction of the railroad along the face of 

 the eastern wall of the gorge affords opportunity to study the rate 

 of erosion during a definite period of time. The accompanying 

 photogravures will illustrate to the eye facts which it is hard to 

 make impressive by words alone. The course of the road is diago- 

 nally down the face of the gorge from its summit for a distance of 

 about two miles, descending in that space about two hundred feet 

 to the outcrop of hard quartzose Medina sandstone. The lower mile 

 of this exposure presents the typical situation for making an estimate 

 of the rate at which the face is crumbling away. 



Beginning at what used to be known as the " Hermit's Cave," 

 near the Catholic College grounds, where the Magara shale is well 

 exposed, and extending to the outer limit of the gorge, the height 

 of the face above the railroad averages one hundred and fifty feet. 

 ISTow, the crumbling away of the superincumbent cliffs gives contin- 

 ual trouble to the road. Three watchmen are constantly employed 

 along this distance to remove the debris which falls down, and to give 

 warning if more comes down than they can remove before trains are 

 due. The seventy feet of Niagara shale, and the equal thickness of 

 shaly Medina rock which underlies the Clinton limestone, are con- 

 stantly falling off, even in fair weather, as any one can experience by 

 walking along the bank; while after storms, and especially in the 

 spring, when the frost is coming out, the disintegration proceeds at a 

 much more rapid rate. Sometimes two or three days are required by 

 the whole force of section hands to throw over the bank the result 

 of a single fall of material. 



At a rate of one quarter of an inch of waste each year the amount 

 of dehris accumulating for removal on the track along this distance 

 would be only six hundred and ten cubic yards per annum — that is, 

 if six hundred and ten cubic yards of mat(>rial falls down from one 



