~t 
142 WEATHERING OF ROCKS. 
been called the “‘ weathering of strata,” and there — 
are examples of it very evident to the most casual 
view throughout our district. In several of these 
strata however, and more especially in limestone, a 
vast aggregation of small blocks (not seldom fossili- 
ferous) rests on the main body of the rock in so 
regularly disposed a manner as to lead to the pre- 
sumption that they were originally so placed, and 
that the rock has not been “‘ weathered” into this 
condition. In some spots, limerock at its surface 
appears cracked into numberless small rhomboidal 
fragments, owing I believe to the access of damp, 
air, and heat, and perhaps owing also to a less 
degree of density than belongs to the interior of the 
stratum. At the period when our strata were dis- 
turbed by subterranean Plutonic convulsions, these 
fragments originally deposited on the solid beds or 
severed by disintegrating causes, were further re- 
moved, and perhaps launched into lower situations. ° 
Again, at the period when a body of waters over- 
spread and swept through the country, many of 
these fragments were carried from the beds to which 
they belonged, and lodged together with clay in 
other positions. Among the fragments which sur- 
mount lime hills, may be discerned portions of rock 
totally different, so that to some extent these 
accumulations are not distinct from those collections 
of debris termed ‘* Diluvium.” But in modern and 
in present times, the original and previous amount 
of dissolution of rocks at their superficies is con- 
tinually being augmented, and in some parts of a 
bed it is carried on much more speedily than in 
others. 
