Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/690

 of appreciable size. The box-stones are to be found in some quantity on the beach at Felixstow, having been washed out of the cliffs, and are also to be seen in the so-called " coprolite diggings." They occur in the "bone-bed" which is exposed in these diggings, and are picked out by the workmen, together with flints and a few other pebbles, from among the smaller phosphatized-clay fragments, and are thrown into heaps by the side of the diggings, when they are sold as "metal" for the roads. With one exception all the masses of sandstone I have seen thus picked out from the diggings have been spherical, oblong or irregular masses about the size of the fist, on an average, or sometimes of an elongated cylindrical form. The exception was in a pit at Trimley, near Ipswich, where I found four blocks of a flagstone shape about a foot and a half square, which contained casts of shells, and seemed to be identical in origin with the box-stones.

It is important to ascertain whether these "box-stones" are all of the same age, "whether any of them may be masses of Eocene, or even Cretaceous sandstone. After examining a vast number of them, I believe them all to be rolled masses of the same arenaceous deposit and of Diestien age. Some of them have a very decided green tint, and vary in the darkness of this coloration. This coloration recalls strongly the black sands of Antwerp, to which it appears they are related, and is due to the same glauconitic constitution. Others of the nodules have a dark reddish-brown tint, particularly those from the sea-beach, and this change of colour is, no doubt, due to the higher oxidation of the contained iron. Lithological evidence is entirely in favour of the community of origin of these rolled masses of sandstone, the only doubtful specimens being those from the pit at Trimley above mentioned. Amongst the stones separated from the " coprolites" by the diggers, fragments of Liassic and of Cretaceous rocks are to be found, but very rarely. There is no chance, it will be admitted on inspection of the specimens, of confounding derived greensand specimens with these box-stones.

The box-stones, being of very porous constitution, are constantly subject to the action of infiltering water, and consequently those which contain shells have, with very rare exceptions, been deprived of the calcareous matter of the shell ; consequently on breaking open such a " box-stone" with the hammer, a very perfect natural cast of the interior of the shell is obtained and also a concave cast of the exterior. Under these circumstances identification of the species of enclosed mollusca is exceedingly difficult ; for even skilled conchologists are not apparently familiar with the appearance of internal casts of the various species which they study. A very useful plan, in those cases which allow it, I have found to consist in taking gutta-percha impressions of the concave casts ; in this way a perfect restoration of the original shell is obtained, and conclusions formed from the internal casts may be corrected. In this way I have got very beautiful impressions of a Conus (Plate XXXIV. fig. 5) (first observed by Mr. Searles "Wood in these nodules), also of a small Cassidaria (Plate XXXIV. figs. 8, 9), which has been hitherto regarded