The Geologist/Volume 5/Notes and Queries, Turtle Remains in the Upper Greensand
Turtle Remains in the Upper Greensand.—The phosphatic nodules of the Upper Greensand of Cambridge are well known to geologists from their extensive commercial use in the manufacture of super-phosphate of lime for agricultural purposes. The nodules have been secreted in or around various organic remains, many of which, such as the bones, were often, probably, broken up before the concretion of the phosphatic matter around them, and both they, and the nodules subsequently, have apparently been not uncommonly subjected to a considerable amount of rolling and degradation. Numerous kinds of shells are common in these nodules, as are bones of pterodactyles and other reptiles. Our attention has lately been drawn to very numerous fragmentary remains of turtles, consisting chiefly of the crania and lower jaws, with numerous fragments of the carapace, ribs, and many vertebræ. The predominance of the skulls and lower jaws in the collection we refer to, which was made by Mr. Farren, of Cam- bridge, and has just been purchased by Mr. Gregory, is probably the mere accidental result of the collecting of what might be deemed saleable specimens, or that these portions being the most readily recognized, attracted attention, while the other fragments of the limbs and body, more obscure in their aspect, were left in nodule-heaps. Professor Owen has made out distinctly, not less than four species, namely,—Chelone sulcimentum, C. altimentum, C. uncimentum, and C. depressimentum. But the point to which we want to draw attention is, the district and the land-shores on which these turtles lived. The Upper Greensand is a marine deposit, and the beds at Cambridge seem closely allied to the grey chalk, especially as that member of the cretaceous group appears developed in Kent and Sussex, and therefore should have been formed under some considerable depth of water.
Now all the Cheloniæ are of littoral habits, and as these greensand-nodules, like the phosphate-nodules from the Gault and Lower Greensand, and all the other deposits from which we have seen them, frequently have oyster and other shells attached to them, it would seem that they had been brought to a hardened state before they were imbedded in the strata where we now find them. We ought therefore to look to some of the older formations as the land whose coasts they inhabited.
The turtles of the Wealden have never been properly collected, and it is with a view to inducing some one to take up the search for them and their comparison with these Upper Greensand fragments, that we have published this note; for to the Wealden lands a priori, it is that we should be inclined to turn for the shores on which these ancient turtles lived, and from which their concreted remains were probably washed down by the tides and currents into the lower depths of the Wealden sea, where some portions of the Upper Greensand were contemporaneously being deposited.