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Inner Hebrides , as in other parts of the British islands, theLiasic deposit appears to have been a muddy one, and un-favourable, in consequence, to the growth of corals. Compa-ratively early in the period, however, a pause took place inthe process of deposition ; massive corals began to form atthe bottom of a clear sea; the term of rest was protracted forages; as one corallum died, another formed over it, until atlength the bed had become several feet thick, and then the de-posit suddenly returned to its old conditions. An arenaceousmud began to be cast down, which insinuated itself into allthe interstices of the bed, as the run lime of the mediaevalbuilders insinuated itself among the loose stones with whichthey filled up the interior portions of their walls. In circum-stances so ungenial the coralites died ; stratum after stratum,—not a few of these richly charged with the peculiar shellsof the Lias,—ammonites, belemnites, and the characteristicgryphsea incurva,—were heaped over them to the depth of se-veral hundred feet. In a few of the overlying strata the samecoral again appeared, but only in small and unfrequent spe-cimens ; and, so far as we yet know, not until the times ofthe Lower Oolite did corals in any considerable abundanceagain live in the seas of the Scottish Oolitic system.
The Lower Oolite, as developed in the neighbourhood ofHelmsdale, 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 So-ciety on a previous occasion, that on examining, some yearssince, a heap of materials collected along the beach in thatneighbourhood for burning into lime, I found that about two-thirds of the whole consisted of fossil wood, and the remain-ing third of a massive fossil corah This coral, also an Isas-trea, is of great size: I have seen specimens which a strongman could scarce raise from the ground; and a specimen onthe table of the Society, selected, however, rather for its fine