126 THE CANADIAN NATURALIST. [April 



the interior of Polythalamia, the glauconite having filled them by 

 " a species of natural injection, which 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." Bailey confirmed these observations, and ex- 

 tended them. He found in various Cretaceous and Tertiary lime- 

 stones of the United States, casts in glauconite, not only of Foram- 

 inifera, but of spines of Echinus, and of the cavities of corals. 

 Besides, there were numerous red, green, and white casts of minute 

 anastomosing tubuli, which, according to Bailey, resemble the casts 

 of the holes made by burrowing sponges (Cliond) and worms. 

 These forms are seen after the dissolving of the carbonate of lime by 

 a dilute acid. He found, moreover, similar casts of Foraminifera, 

 of minute mollusks, and of branching tubuli, in mud obtained from 

 soundings in the Gulf-stream, and concluded that the deposition of 

 glauconite is still going on in the depths of the sea.* Pourtales 

 has followed up these investigations on the recent formation of glau- 

 conite in the Gulf-stream waters. He has observed its deposition 

 also in the cavities of Millepores, and in the canals in the shells of 

 Balanus. According to him, the glauconite grains formed in For- 

 uminifera lose after a time their calcareous envelopes, and finally 

 become " conglomerated into small black pebbles," sections of which 

 still show under a microscope the characteristic spiral arrangement 

 of the cells.f 



It appears probable from these observations that glauconite is 

 formed by chemical reactions in the ooze at the bottom of the sea } 

 where dissolved silica comes in contact with iron-oxide rendered 

 soluble by organic matter ; the resulting silicate deposits itself in 

 the cavities of shells and other vacant spaces. A process analogous 

 to this in its results, has filled the chambers and canals of the 

 Laurentian Foraminifera with other silicates ; from the compara- 

 tive rarity of mechanical impurities in these silicates, however, it 

 would appear that they were deposited in clear water. Alumina 

 and oxide of iron enter into the composition of loganite as well as 

 of glauconite; but in the other replacing minerals, pyroxene and 

 serpentine, we have only silicates of lime and magnesia, which wer e 

 probably formed by the direct action of alkaline silicates, either 



* Silliman's Journal [2] xxii, 280. 

 f Report of United States Coast-Survey, 1858, p. 248. 



