426 Miscellaneous, 



geologists. Ill a notice given by this distinguished observer upon 

 the nature of the matrix of the bones of the Zeuglodon from Ala- 

 bama (see Berhn Monatsbericht, February 1855), he says : — 



*' That greensand, in all the numerous relations in which I have 

 as yet examined it, has been recognized as due to the filling -up of 

 organic cells, as a formation of stony casts (Steinkernbildung) mostly 

 of Polythalamia, was stated in July of the preceding year." He 

 then refers to the Nummulite limestone of Traunstein in Bavaria, 

 as rich in green opal-like casts (Opalsteinkernen) of well-preserved 

 Polythalamian forms, and mentions them as also occurring, but 

 more rarely, in the Glauconite limestones of France. He then 

 proceeds to give an account of his detection of similar casts in the 

 limestone adhering to the bones of the Zeuglodon from Alabama, 

 and states that this limestone abounds in well-preserved brown, 

 green, and whitish stony casts of recognizable Polythalamia. This 

 limestone is yellowish, and under a lens appears spotted with green. 

 These green spots are the greensand casts of Polythalamia, and they 

 often form as much as one-third of the mass. By solution in dilute 

 hydrochloric acid, the greensand grains are left, mixed with quartz- 

 ose sand, and with a light yellowish mud. The latter is easily 

 removed by washing and decantation. The casts thus obtained are 

 so perfect, that not only the genus, but often the species of the 

 Polythalamia can be recognized. Mingled with these are frequently 

 found spiral or corkscrew-like bodies, which Ehrenberg considers as 

 casts of the shells of young moUusks. 



With reference to the perfection of these casts of the Polythalamia, 

 and the light they throw upon the structure of these minute animals, 

 Ehrenberg remarks : — 



" The formation of the greensand consists in a gradual fiUing-up 

 of the interior space of the minute bodies with a green-coloured, opal- 

 like mass, which forms therein as a cast. It is a peculiar species of 

 natural injection, and is often so perfect, that not only the large and 

 coarse cells, but also the very finest canals of the cell-walls, and all 

 their connecting tubes, are thus petrified and separately exhibited. 

 By no artificial method can such fine and perfect injections be ob- 

 tained." 



Having repeated the experiments of Ehrenberg upon the Zeuglodon 

 limestone, I can confirm his statements in every particular, and would 

 only add, that besides the casts of Polythalamia and small spiral 

 mollusks, there is also a considerable number of green, red, and 

 whitish casts of minute anastomosing tubuli, resembling casts of the 

 holes made by burrowing sponges (Cliona) and worms. 



In the Berlin Monatsbericht for July 1855, Ehrenberg gives an 

 account of very perfect casts of Nummulites, from Bavaria and 

 from France, showing not only chambers connected by a spiral 

 siphuncle, but also a complicated system of branching vessels. He 

 also gave at the same time an account of a method he had applied 

 for the purpose of colouring certain glass-like casts of Polythalamia, 

 which he had found in white tertiary limestone from Java. This 

 method consists in heating them in a solution of nitrate of iron, by 



