372 
[Assembly 
lake can be drained no faster than this rock is worn off by the action of 
the water. The force of the river is gradually decreasing, and of course 
the recession will be more gradual from this cause. But for another 
reason, the rate of recession will be incalculably less as we progress 
southward. At the present time the falls recede principally by the ac- 
tion of the water on the soft shale below, wearing it rapidly away and 
leaving the limestone unsupported, when it falls of its own weight. — 
After the falls recede about two miles farther, the shale will have disap- 
peared below the level of the river, and consequently the water will 
descend over a solid wall of limestone; after this period the falls will 
recede only by the slow wearing of this rock. 
The accompanying wood cut represents a section of the rocks at Lew- 
iston. 1, the upper limestone; 2, shale; 3, limestone; 4, red marl and 
sandstone; 5, hard siliceous sandstone; 6, red marl. The surface of 
No. 1, at the top of the ridge, is worn and scratched, as if by the action 
of running water, carrying with it pebbles or hard materials. The 
shale. No. 2, is worn off at a gradual slope; the limestone. No. 3, has 
its projecting surface worn and scratched like the upper limestone. The 
hard sandstone, No. 5, projects much farther, and is also worn and 
scratched. At the termination of this stratum is a small valley, and 
beyond it a large mound of fragments of the sandstone and two lime- 
stones; the former most abundant. These fragments are thrown to- 
gether in the greatest confusion, and bear conclusive evidence of the ac- 
tion of a powerful current. Dr. Scovill has erected a large house and 
several other buildings on the top of this elevation, (A,) from the im- 
bedded masses; a well was dug seventy feet deep in the same place, 
without finding the termination of the deposit. Since the period of 
this deposition, the river has been reduced to narrower limits, and has 
worn its channel in the strata here represented. 
