The erratics of the Cambridge Greensand.

Abstract

Fossil Wood from the Cambridge Greensand. —In discussing the mode of transport of the erratics over the Greensand sea, Dr. Hawkes invoked the aid of drifting vegetation, and especially roots of trees, though he remarked that no tree remains had been reported from the deposit. It may therefore be of interest to place on record, in addition to the fossil resin which Dr. Hawkes mentioned, some instances of petrified wood found in the Cambridge Greensand. Two of these have come to light in the Sedgwick Museum since the reading of the paper, and I am indebted to Dr. Hawkes for drawing my attention to them. One specimen (Sedgwick Museum no. 209), labelled " Cambridge Greensand, Hauxton ", is a piece of phos-phatized secondary wood about 15 cm. in length and up to 5 cm. in diameter; part of it is riddled with Teredo -borings. The anatomy, as revealed in thin sections, shows it to be a conifer referable to the form-genus Cedroxylon , but some important details, such as the pitting on the walls of tracheids and medullary ray cells, are on the whole rather poorly preserved, so that a complete botanical description and a specific diagnosis are scarcely possible. Interesting features include the rare occurrence of traumatic vertical resin-canals, and the irregularity of the growth-rings. There is no resin-parenchyma, but black cell contents in some of the tracheids are probably resinous in origin; it does not, however, seem likely that a tree of this type would have produced the lumps of amber