In the upper chalk every one has seen the layers of flint, and marked their singular distribution, in layers; and here we would add, that the existence of flint in chalk is one of those hard nuts which geology has not yet cracked. The geologist, the chemist, and the zoologist have all puzzled themselves in vain to find a truly satisfactory origin for these nodules of siliceous matter. We have heard it suggested that they may be _coprolites_; but no one who examines the texture of a flint, can hold that theory, to say nothing of the idea that the coprolites have been preserved, while the animal remains have perished. We may sum up all we have to say about flints in the following words, from that useful little book, Chambers’s “Rudiments of Geology:” “_The formation of flint_, within a mass so different in composition as chalk, is still in some respects an unsolved problem in geology. It occurs in nodular masses of very irregular forms and variable magnitude; some of these not exceeding an inch, others more than a yard in circumference. Although thickly distributed in horizontal layers, they are never in contact with each other, each nodule being completely enveloped by the chalk. Externally, they are composed of a white cherty crust; internally, they are of a grey or black silex, and often contain cavities lined with chalcedony and crystallized quartz. When taken from the quarry they are brittle and full of moisture, but soon dry, and assume their well-known hard and refractory qualities. Flints, almost without exception, enclose remains of sponges, alcyonia, echinida, and other marine organisms, the structures of which are often preserved in the most delicate and beautiful manner. In some specimens the organism has undergone decomposition, and the space it occupied either left hollow, or partially filled with some sparry incrustation. From these facts, it would seem that flints are as much an aggregation of silex around some organized nucleus, as septaria are aggregations of clay and carbonate of iron. This is now the generally received opinion; and when it is remembered that the organisms must have been deposited when the chalk was in a pulpy state, there can be little difficulty in conceiving how the silex dissolved through the mass would, by chemical affinity, attach itself to the decaying organism. Chalk is composed of carbonate of lime, with traces of clay, silex, and oxide of iron; flint, on the other hand, consists of 98 per cent. of pure silex, with a trace of alumine, oxide of iron, and lime. Silex is quite capable of solution: it occurs in the hot-springs of Iceland and most thermal waters; has been found in a pulpy state within basalt; forms the _tabasheer_ found in the cavities of the bamboo, and the thin pellicle or outer covering of canes, reeds, grasses, &c.; and siliceous concretions are common in the fruits and trees of the tropics. All these facts point to a very general