88 GEOLOGICAL MEMOIRS. 



their localities. The number of species described amounts to thirty ; 

 but he states that every fresh investigation has increased this number, 

 and has also tended to confirm the volcanic character of the rock*. 



These thirty organic bodies, associated with very minute frag- 

 ments of cellular glassy pumice greatly resembling them, so com- 

 pletely make up the whole mass of this Patagonian rock, especially 

 at New Bay, that either the shells or fragments of them can be de- 

 tected in every little morsel not larger than a pin's head. It is also 

 perfectly clear that they have been subjected to a high temperature, 

 which has burst them asunder, bent, polished and altered them. It 

 is even probable that the glassy crushed fragments are also derived 

 immediately from these organic products ; but there are here and 

 there, besides these, green crystals resembling augite. 



This mass chiefly consists of species which inhabit salt water, and 

 of these many have been long known and are widely extended 

 through the ocean ; but several of them are new and peculiar, and 

 resemble in shape small stars. Nearly half of them are the siliceous 

 particles of marine sponges whose forms are known, and of which 

 we are in some cases acquainted with the origin. 



The Patagonian rock thus described is therefore manifestly a sea- 

 bottom which has been subject to volcanic action. 



In this case, as before, the spicules of sponges, which are always 

 detached and fragmentary^, can neither have penetrated the volcanic 

 tuff, nor can they have been there developed in a fragmentary state, 

 while such a notion is still less tenable with respect to the infusorial 

 animalcules. A merely elevated sea-bottom which had not been 

 exposed to intense heat must necessarily have exhibited various or- 

 ganic bodies, as in Oran, Sicily and Virginia, containing entire 

 sponges, corals, foraminifera and shells, and would not merely con- 

 sist of fragments of pumice and of siliceous-shelled infusoria. Fora- 

 minifera and all other calcareous remains are here entirely absent, 

 and they, as well as the argillaceous particles on the sea-bottom, have 

 probably served partly as a flux for reducing the fused siliceous 

 particles, and have partly been decomposed to form the gypsum. 



[The author then proceeds to describe several infusoiial remains occurring in the 

 loamy earth of Patagonia and the banks of the Plata, whence were obtained the 

 gigantic mammalian remains of Edentates and other animals brought home by Mr. 

 Darwin and described by Professor Owen. These are almost entirely of fresh- 

 water origin, and differ therefore from those found in the rock already alluded to. 

 He next mentions two kinds of Phonolite, the trass of the Siebengebirge, and the 

 ashes under which Pompeii is biuied, as all containing infusorial remains, although 

 the number of species is not considerable ; and he concludes by alluding to a 

 singular instance of a body apparently organic but not infusorial, found in the 

 trachyte of Zimapan in Mexico. These matters not bearing directly upon the 

 principal point in question in this memoir are here omitted. — Ed.] 



* The species of Polygastrica (infusorial animalcules) amount to seventeen, and 

 the Phytolitharia are thirteen. They are thus distributed : — 



Polygastrica. Phytolitharia. Total. 



Port St. Julian 10 8 18 



Port Desire 13 7 ......... 20 



New Bay 2 ......... 1 3 



