II.—Creechbarrow in Purbeck.—No. 2 (continued)

Extract

Varieties of the Creechbarrow Limestone.—There are considerable extremes in this respect, ranging from a soft marly deposit, which soils the fingers like whitening, to a hard compact rock, which takes a good polish. Unquestionably the most dense and compact lime-stone is that near the summit, whilst the soft marly beds are on the northern slope, and especially near the 500 feet contour, where some of them are earthy and contain a considerable amount of impurity, so that they may at least be called marly limestones. On the other hand, there are compact white limestones, where nests of dog-tooth spar form no inconsiderable portion of the mass. Quartz grains may be noted on most of the weathered surfaces.

The more compact and denser limestones, which prevail near the summit, may be roughly divided into non-pisolitic and pisolitic rocks. Thus, for instance, I have before me (Group 1) specimens of a very heavy and partially calcitic rock. It is a hard whitish limestone without pisolites, but largely interspersed with buff-coloured patches, not unlike some dolomites. Calcitic nests and strings occur, and also strings and stars of black oxide of manganese: the external surface is rough and somewhat honeycombed, and full of curious impressions, some of which may have had an organic origin.

Group 2 comprises those specimens where the pisolitic character is indicated, but not very obviously. A characteristic specimen may be described as follows:—A large fragment of a creamy white tufaceous limestone, with specks and threads of black oxide of manganese in places: flattened pisolitic bodies in brownish calcite are numerous, but not very distinct.