And this seems a fitting opportunity to the writer to put on record the fact that many of the most wonderful remains found in the Oxford Clay and the neighbouring Kimeridge Clay are due to the discoveries of brickmakers. Without their valuable aid scientists would be quite unable to clearly depict the life of those remote epochs. We have mentioned Peterborough; some most interesting remains have been found in the clays near that town during the past few years. To appreciate this let the reader visit the fossil reptile gallery of the British Museum (Natural History), at South Kensington. One of the most recent acquisitions, set up a year or two ago, is the skeleton of a young _Plesiosaurus_--without doubt the most perfect specimen in the world of its kind--from Peterborough. The _Plesiosaurus_ was a large swimming reptile, with paddles, and a long neck. We mention these things not only to instil philosophical interest in such brick-earths, which may be reflected upon after business hours, but to impart some idea of the extreme remoteness of the epoch from the human point of view, and to insist on the immensity of the intervening time throughout which circulating underground waters--even in such an impervious material as stiff clay--may have exerted chemical action. The “mineralisation” of the fossils is an eloquent witness of the effect of such changes. The reader will perceive from this that there is scant possibility of soluble salts being present in such marine clays; and the geological circumstances are fully borne out by the results of hundreds of chemical analyses of thick marine clays. The invertebrate fossils more particularly testify to the marine origin of the clays, and are thus invested with considerable practical interest. The man whose duty it is to determine the persistence, or otherwise, of valuable marine brick-earths has thus a much easier task than when called upon to decide the value of a large tract of land for brickmaking purposes, of fluviatile origin. Finally, brick-earths do not, except in extremely rare instances, vary materially in character when dug into horizontally, thus every opportunity is afforded to the manufacturer for making an unvariable quality brick, tile, or drain pipe. It should be borne in mind, however, that these clays often weather a brown colour, which on being dug into changes to a bluish-black tint, the latter being the unaltered and best portion as a rule. The only practical advantage the worker of a superficial river deposit possesses over his neighbour using thick marine clay is in the great range of variation in materials disclosed in the former kind of pit. By judiciously mixing the different beds he may be able to live well where the worker of marine clays, especially where the clay is too stiff, or contains too much lime, “comes to grief.” A good marine clay is a great boon, a bad one cannot be remedied other than by the sacrifice of much money. CHAPTER IV.