84 BAILKY, ON GREENSAND. 



observer upon the nature of the matrix of the bones of the 

 Zeuglodon from Alabama (see ' Monats-Bericht/ Berlin, 

 February, 1855), he says : 



" That Greensand, in all the numerous relations in which I 

 have as yet examined it, has been recognised as due to the 

 filling up of organic cells, as a formation of stony casts (Stein- 

 kernbildung), 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 Hmestone abounds in well- 

 preserved brown, green, and whitish stony casts of recogni- 

 sable Polythalamia. This limestone is yellowish, and under a 

 lens appears spotted with green. These green spots are the 

 Greensand casts of the Polythalamia, and they often form as 

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

 hydric acid, the greensand grains are left, mixed with quartzose 

 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 recognised. Mingled Avith these 

 are frequently found spiral, or corkscrew-like bodies, Avhich 

 Ehrenberg considers as casts of the shells of young moUusks. 



With reference to the perfection of these casts of the Poly- 

 thalamia, and the light they throw upon the structure of these 

 minute animals, Ehrenberg remarks : 



" The formation of the Greensand consists in a gradual 

 filling up of the interior space of the minute bodies with a 

 green-coloured, opal-like mass, Avhich forms therein as a cast. 

 It is a peculiar species of natm'al 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 

 obtained." 



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 moUusks, there is also a con- 

 siderable number of green, red, and Avhitish casts of minute 

 anastomosing tubuli, resembling casts of the holes made by 

 burrowing sponges (Cliona) and worms. 



