The Wiltshire archaeological and natural history magazine . Salisbury Plain, and one of my colleagues is now engagedin tracing it over the country between Marlborough and Melbourn Rock is not a compact homogeneous Chalk, butconsists of layers of small nodules of a hard compact chalk em-bedded in a chalk of coarser texture and largely composed of frag-ments of Inoceramus shell. This structure is shown very clearly inthe slide from which Fig. 4 is taken, and is fairly well shown inthe engraving, which has been made from a photograph taken byMr. W. Freshwater. The dark portions are the
The Wiltshire archaeological and natural history magazine . Salisbury Plain, and one of my colleagues is now engagedin tracing it over the country between Marlborough and Melbourn Rock is not a compact homogeneous Chalk, butconsists of layers of small nodules of a hard compact chalk em-bedded in a chalk of coarser texture and largely composed of frag-ments of Inoceramus shell. This structure is shown very clearly inthe slide from which Fig. 4 is taken, and is fairly well shown inthe engraving, which has been made from a photograph taken byMr. W. Freshwater. The dark portions are the nodules of compactChalk, and the other part is the shelly Chalk, one large fragmentof shell extending right across the lower part of the figure. The higher part of the Middle Chalk is a typical white Chalk, sopure, and containing so few flints or fragments of shell that it isoften used to make whitening. The material of which it consists is sofine that even under the microscope it looks like fine white powder, 326 The Geology of Devizes. I Fig. 4 Fig. Figs. 4 and 5.—Structure of Melbourn Rock and of Chalk Rock(magnified fifty times). but in it are scattered immense quantities of small round bodieswhich are either the cells of Foraminifera or of some allied are minute creatures which abound in all the seas andoceans of the present day, some living in shallow water, and someonly in the open ocean. They extract carbonate of lime from thewater, and construct tiny shells perforated by small holes, and theseshells, either perfect or in fragments, have contributed largely to allparts of the Middle and Upper Chalk. A common form (Globi-gerina) is seen in the lower part of Fig. 6, and the small roundbodies occurring in the surrounding material are nowhere sonumerous and so robust as in this part of the Middle Chalk. Thequarry below the butts on Roundway Hill is opened in this Chalk,and it forms the steepest part of the slopes round Oldbury Hill,Morgans Hill,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
