22 
THE GEOLOGIST. 
layers to form strata, or round certain centres to form nodules, in a 
manner analogous to that in which metals crystallize themselves from 
their vast dispersion throughout the substance of the globe. It is 
quite true, we know but little of the effects of such forces, exerted 
incessantly during countless ages, but we have good reason to believe 
that they have acted ; and may we not, with some probability, refer 
to them such phenomena as 1 have described ? 
Let it be remembered, that two distinct facts demand explanation : 
— 1st, the preponderance of lime in certain comparatively thin strata ; 
and, 2ndly, the not less remarkable absence of lime in strata enor- 
mously thick. Are not these facts correlative ? Is it not probable 
that the lime which once composed part of the fossils in the earthy 
strata has been agglomerated in these bands and nodules, by a process 
on a large scale analogous to that which takes place in the formation 
of flints, and, in some degree, like the aggregation of the metals ? 
Dear Sir, — I enclose the above suggestive note by my friend the 
Rev. J. La Touche, a working geologist, trained in the the Ludlow 
school. 
I cannot say I agree with him in his larger generalization, for there 
is no doubt whatever of the actual deposit of these beds of limestone, 
again and again, over the same area, with interruptions marked by the 
deposit of shale. Nay, strange as it may seem, the beds of limestone, 
crammed with fossils, often alternate closely with beds of shale, in 
which one can hardly detect a fragment of a fossil. In these, and in 
most cases, I believe, a band of limestone means — a period of " rest." 
The shale beds are signs of a 
more turbid action of the 
water. 
But then, his observation 
is a good one for a great many 
cases. No one who has stu- 
died the old limestones can 
believe they were deposited 
'quite as we now find them — 
full of strange lenticular 
shapes, now crowding out the 
shale beds, now completely 
enveloped in them. Such 
cases as the following are not 
at all uncommon. 
We may be well assured of two tilings : — 1. There luas a bed 
of limestone, for the nodules lie in horizontal planes, and are made 
up of fossils in many cases. 2. The subsequent action has increased 
the size of the limestone band, and given it a nodular form by at- 
traction round central points. 
The old proverb, "He that hath shall have more," is, I believe, 
strictly applicable in such cases. The band, comparatively rich in 
Fig. 1. — Nodules of Limestoue in Shale. 
