OOLITIC SYSTEM OF SCOTLAND. 365 
deposit appears to have been a muddy one, and unfavorable, in 
consequence, to the growth of corals. Comparatively early in 
_the period, however, a pause took place in the process of deposi- 
tion , massive corals began to form at the bottom of a clear sea; 
the term of rest was protracted for ages; as one corallum died, 
another formed over it, until at length the bed had becomie sey- 
eral feet thick, and then the deposit suddenly returned to its old 
conditions. An arenaceous mud began to be cast down, which 
insinuated itself into all the interstices of the bed, as the run 
lime of the medizval builders insinuated itself among the loose 
stones with which they filled up the interior portions of their 
walls. In circumstances so ungenial the coralites died; stratum 
after stratum, — not a few of these richly charged with the 
peculiar shells of the Lias,— ammonites, belemnites, and the 
characteristic gryphea incurva,— were heaped over them to 
the depth of several hundred feet. In a few of the overlying 
strata the same coral again appeared, but only in small and 
unfrequent specimens; and, so far as we yet know, not until 
the times of the Lower Oolite did corals in any considerable 
abundance again live in the seas of the Scottish Oolitic system. 
The Lower Oolite, as developed in the neighborhood of 
Helmsdale, on the north-eastern coast of the kingdom, is com- 
paratively rich in corals; at least, if species be not numerous, 
individual specimens are far from rare. I stated to the Society 
on a previous occasion, that on examining, some years since, a 
heap of materials collected along the beach in that neighbor- 
hood for burning into lime, I found that about two-thirds of 
the whole consisted of fossil wood, and the remaining third of 
a massive fossil coral. This coral, also an Isastrea, is of great 
size: I have seen specimens which a strong man could scarce 
raise from the ground ; and a specimen on the table of the 
Society, selected, however, rather for its fine form than for its 
bulk, measures full eighteen inches in length, by about a foot 
31* = 
