When we applied for a grant to aid in the working out of the Purbeck fossil
Characeæ
, we thought it was only a question of studying the anomalous structure of one, or perhaps of two, species, of which we had already gathered together a number of silicified specimens. It was thought that by polishing a large number of surfaces, or cutting slides of this cherty material, we should discover the links connecting the different parts of the plant. Further visits to Dorset provided, however, an enormous amount of new material, and the discovery of similar remains in a hard, close-grained limestone opened up new and better methods of research. The silicified
Characeæ
showed in section curious structures, so mineralised and so difficult to interpret, that it was most desirable to obtain specimens in the round, in order better to study their anatomy. This the calcareous blocks enabled us to do, though, on the other hand, some of the chert specimens preserved delicate non-calcified structures which were missing in the limestone. On treating some of the limestone blocks with a steady drip of slightly acidulated water, the results were so surprising that we determined to devote most of the amount granted to the work of cutting all the more promising blocks into a series of thin slabs. Numerous slices were cut, and one side oi each was then subjected for many hours to the drip. Most of the blocks proved to be partially and irregularly silicified, others were more or less dolomitised, a few were partly impregnated with a brown hydrocarbon. The drip rapidly attacked the pure calcite parts of the matrix and also the crystalline fossils, such as the mollusca, leaving the mineralised areas standing up. This, of course, was what one would expect. But more remarkable was the discovery that a great part of the characeous remains were not now pure calcite. Though not visibly different from the matrix they are so mineralised as to resist the acid and to stand out in bold relief from the etched surface of the slab of limestone. We have even been able completely to remove fruits and stems from the matrix, though, as a rule too long a continuance of the acid drip does at last affect the fossils, and it if better to let well alone when a specimen shows in sufficient relief.
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