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Preliminary Report on the Purbeck Characese. 

 By Clement Eeid, F.R.S., and J. Groves. 



(Eeceived January 7, 1916.) 

 [Plate 8.] 



When we applied for a grant to aid in the working out of the Purbeck 

 fossil Characece, 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 Characece 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 of 

 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 is 

 better to let well alone when a specimen shows in sufficient relief. 



