GEOLOGY. 303 



defined springs, but the surface is filled with innumerable cracks or fissures 

 from four to eighteen niches in width, communicating with subterranean cavi- 

 ties or chambers, through which the boiling water is forced with great velo- 

 city, and producing a noise closely resembling that produced by the wheels 

 of a powerful steamer upon the water. A singular feature is, that in large 

 tracks but a few feet from each other, the boiling water is seen flowing hi 

 opposite directions ; and in others changing from one direction to another at 

 intervals of a few minutes. In many places the waters overflow the surface, 

 but more generally traverse the crevices at various depths from the surface, 

 generally in view, but sometimes so deeply within as not to be distinguished, 

 whilst the ceaseless roaring, splashing, and hissing is heard in every direction. 

 And jets of steam that will scald the hand instantly on application, are here 

 and there forced through the openings and fissures, high above the surface of 

 formation, and with great violence. There is one place more remarkable, if 

 possible, than others ; it is where the surface of the rocky deposit is unbroken, 

 yet loudly distinct beneath is heard the roaring as of a strong blast furnace. 

 IsTot a drop of water is visible here, but the rock or deposit on which the 

 spectator stands, is actually burning hot ; the bare hand can scarcely be held 

 upon it for a moment. Morning and evening, when the air is cold and still, 

 the whole is shrouded with steam and vapor. In many places there are 

 small deposits of sulphur that will ignite by the application of a match ; in 

 others the strongest alum was found ; and yet others, an alkaline substance 

 so concentrated as to destroy in a short tune a linen handkerchief in which a 

 specimen had been wrapped. The country in the immediate vicinity- bears 

 unmistakable evidence of the effect of powerful volcanic action masses of 

 vitrified rocks, cinders, the ordinary coarse conglomerate scoria of extinct 

 volcanic craters ; and not a few specimens were obtained of the lightest, 

 pumice stone ever seen." 



OX THE-OEIGIX OF GREENSAND, AXD ITS FOR3IATIOX IX THE 

 OCEAXS OF THE PRESENT EPOCH, BY PROF. J. W. BAILEY. 



As an introduction to the subject of this paper, it is proper to refer to various 

 observations which have been made of facts ultimately related to those which 

 I wish to present. That the calcareous shells of the Polythalamia are some- 

 times replaced by silica, appears to have been first noticed by Ehrenberg, who 

 says : 



" I may here remark that my continued researches on the Polythalamia of 

 the Chalk have convinced me that very frequently in the earthy coating of 

 flints, which is partly calcareous and partly siliceous, the original calcareous 

 shelled animal forms have exchanged their lime for silex without undergoing 

 any alteration in figure, so that while some are readily dissolved by an acid, 

 others remain insoluble ; but hi chalk itself, all similar forms are immediately 

 dissolved." 



The first notice of casts of the cells and the soft parts of the Polythalamia 

 was published by myself in the Am. Jour, of Science for 1845, where I stated 

 as follows : 



" The specimens from Fort "Washington presented me with what I believe 



