_— 
JANUARY 4, 1884.] 
accumulates and stands, and as a consequence 
the grains of the rock in immediate contact 
are loosened, and, on the evaporation of the 
water, blown away. Thus the depressions 
which were at first, 
perhaps, only a frac- 
tion of an inch, are 
deepened, and, by de- 
grees, basins of as 
much as a foot in 
depth are eaten out. 
These are -often so 
regular in outline, and 
with such smooth 
sides, that they might readily be mistaken for 
pot-holes ; and, indeed, it was such that I first 
considered them, and was puzzled to account 
for the peculiar 
channel in which 
the waters produ- 
cing them must 
have flown. _A dis- 
tinguishing feature 
of these depres- 
sions, however, is 
that each one has 
an outlet cut down 
to near the bottom of the cavity; and this is 
easily accounted for, on the theory of their 
subaerial origin, by considering, that, once 
such a basin started, the overflow would 
always pass off over the lowest edge, and as 
the basin increased in depth, by continued 
dissolving action, so would the outlet also. 
A further confirmation of this is furnished 
by the facts, that in inclined rocks the out- 
let is always towards the lower rim, and the 
bottom of these cavities is either horizontal or 
sloping towards the outlet. In the bottom is 
also generally accumulated a small amount of 
gravel and sand recently loosened from the bed. 
These basins are of all sizes, up to three feet 
Fie. 3.— Weathering across 
the plane of stratification. 
) 
- 
payll 
Vo 
/}) 
i - 
i 
i+ 
Fie. 4. — Enlargement at end of 
fissure. 
Fig. 5.— The results of superficial weathering in the plane of 
stratification. : 
and more in diameter. ‘Their shapes are va- 
ried, — sometimes circular, sometimes oblong, 
—with gently sloping sides, or steep, even re- 
SCIENCE. 13 
curving ones, according to the character of the 
rock. They are frequently connected in strings 
by narrow channels, like a miniature lake sys- 
tem; and, with the enlargement of these chan- 
nels, a simple, deep groove across tlie rock 
results, all this action combining to give the 
rock a very rugged appearance. 
The, very preponderance of silica grains in 
this rock, to the exclusion of any good cement- 
-ing-material, is probably one of the chief 
reasons for its decay. Rain-water is, without 
doubt, one of the most active agents ; but the 
secretions from the thick growth of moss and 
lichens, which frequently covers the surface 
and penetrates into the cavities of the rock, 
have probably also their effects. The deep 
gashes produced by the action of the rain- 
water offer excellent opportunities for frost to 
continue the work of destruction ; the ice form- 
ing in these clefts, and, by its prying action, 
completing the separation of the already par- 
tially divided mass. 
As a consequence of this wide-spread weath- 
ering process, large continuous outcrops are 
rarely found. Collections of huge blocks gen- 
erally mark their site; and the thick accumu- 
lations of smaller fragments, which are so 
frequently found over conglomerate areas, 
eee : 
SS La, = 
ee Peg AGN ULL L 7 
arm ee seh 4 eae 
~ 4 vet 
ES, — 
See 
_— — a 
| VW, = i 
\ Sil ZB = 
\ — =— — 
‘ P a 
v 
\ 7 La? e A —— 
i} Ny “ NG a x , ate 
\ ) y F 
Wri eee aS i ft rr ait “yf 
Pa 2 | H))) Wee 
\ a Tees = dj YEP aif BeewZ, 
=> wh oan ZZ fi (ore 7, 
‘So Se Ys ia oN ZG } 
\ = IG eae) 
= i Qe= : 
_— Sp we ——~— —-F== = 
— a LE 
Cae 4 es 
Sy ee eid SS 
—_~——— 
result, without doubt, from the further subdi- 
vision of these larger blocks. 
The products of decay either accumulate in 
place, are washed down by streams, or blown 
away by the wind. On the top of Broad Moun- 
tain, and elsewhere, the disintegration in sifu, - 
I am informed, is so great that the loose rock 
is dug out as gravel; and, in valleys watered by 
streams flowing down from conglomerate ridges, 
deep deposits of siliceous sand are found, val- 
uable for building-purposes. 
The decay of the sandstones and shales, as- 
sociated with or underlying the conglomerate, 
is even more pronounced than in that rock. 
Changes of color, especially from the greenish 
tints to red, brown, and yellow, are the most 
