59
ON THE MICROSCOPICAL EXAMINATION OF SOME BRACKLESHAM BEDS.
By T. Rupert Jones, F.G.S.
In Vol. I of the 'Geologist,' at page 249, was published a paper on the preparation of sands, clays, and chalk, for microscopical purposes, under the heading of "Geological Manipulations;" and, as both pleasure and geological profit are to be obtained from the exact examination of various fossil-bearing deposits, both as to their constituents and their contents, I beg to offer you an example of the results of such an examination of some tertiary beds from Bracklesham. These notes I have had by me several years, and their shortcomings are so great in some respects that I should not send them, were it not that they may serve as a plan to some young careful observers who might feel inclined to enter upon the strict examination of some definite series of fossiliferous strata. What the series under notice is deficient of, is a statement of the exact relationship of these several deposits, examined nearly twenty years ago. I received the materials at that time from a friend who was collecting "Bracklesham fossils,"—a term which will be more definite, now that the Rev. O. Fisher, F.G.S., has indicated the exact limits of the Bracklesham formation.[1]
The specimens were chiefly, I believe, from Bracklesham and Selsea; but some may have been brought from the Isle of Wight. By the presence of certain fossils, however, in some of the deposits, their exact place may probably be determined. However deficient in these stratigraphical requirements the following account of the deposits may be, they will serve the purpose here intended, namely, to show young beginners what to look for in sands and clays. Instructions have been already given as to how such materials are to be examined, in the first volume, p. 249.
The careful microscopical examination of a good series of successive deposits, in the way that Ave propose, cannot but be useful both to the geologist and the palæontologist. The conditions of deposit will be elucidated by the proportions of fine and coarse materials in the beds; especially if these be traced along a considerable tract by the examination of many samples of the deposit, through its variations from clay to sand (or vice versâ), or in its changes from an argillaceous or arenaceous to a calcareous condition. Such variations are not always recognized with sufficient exactness by the eye or by the pocket-glass, and require mechanical, if not chemical, analysis; recourse being had to the aid of acids in determining the relative proportions of lime and other constituents. Except by careful separation in water, and patient sorting and picking, the minute shells and other fossils cannot be obtained in anything like a fair average; and year by year the Foraminifera, Entomostraca, Bryozoa, and the small
- ↑ See Report of the Geological Society's Proceedings, Dec. 4th, 1861.
