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Introduction.—The Upper Limestones of North Ayrshire are divided into four distinct series of beds by the intervention of shales and flaggy sandstones, giving to each an independent character, both physically and in extent of area. They are all rich in fossil remains, but, with the exception of the lower bed of the series, they are of small commercial value, and the collector has not therefore the opportunity of searching quarries, as in cases where the limestones are more extensively worked. However, from the openings made by, and the sections exposed in, the various water-courses, a fair collection of their fossils has been obtained, and to all appearance the series are as rich as the Lower Limestone beds, both in quantity and variety of their organic remains. They differ, however, from them in the proportions they contain of the same classes of fossils, as for instance corals and crinoids, in which the Upper beds are poor both in genera and species when compared with the rich deposits of the Lower Limestones. Full lists of the fossils are appended to this paper.

Highfield Limestone.—The first, or lower, bed of the series is a deposit of limestone and calcareous shales known as the Highfield Limestone, from being largely wrought at the place of that name. From a similar reason it is also known in a neighbouring locality as the Swindridge Limestone. It is divided from the Lower Limestone series by about 120 fathoms of strata, which hold the workable coals and ironstones of

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