ACADEMY OF NATURAL SCIENCES. 321 



Post-pliocene epoch, and seem to have continued their existence nearly, if not 

 quite, down to the present day. 



So far the facts are very simple, and the principal results of our detailed 

 microscopic examination of these infusorial deposits will be. the knowledge of 

 the range of the different species which occur in them, and the relations of the 

 various forms to those now living, either in this region or in other parts of the 

 world. This the extent of our collections will give us better opportunities to 

 do than others have yet had. 



There is a point, however, of great interest connected with these deposits, in 

 regard to which I desire to make some remarks at this present time, aud on 

 which I consider that our explorations are capable of throwing some light. 



Ehrenberg has recently * examined a specimen collected many years ago, in 

 the Toluca Valley, Mexico, by the well-known mining engineer Burkart, of 

 what he denominates a " Phytolitharien Tuff, - ' or phytolithic tufa, aud which 

 came to him labeled " Trachytic Tufa, from Toluca Valley, quere, whether 

 pumice-like or infusorial." Of this, Ehrenberg says : " It is a silver-gray, easily 

 crumbled, gritty tufa, which does not effervesce with acids, and which, when 

 heated, becomes darker, but not black, aud then assumes a light-browuish color." 

 The microscopic analysis of it showed that it was made up to a large extent of 

 phytolitharia, which probably belong chiefly to the grasses, and between them 

 lie scattered a comparatively small number of bacillaria. All are fresh-water 

 forms. 



In his remarks on this material, Ehrenberg recalls the other specimens of in- 

 fusorial tufas, which have been examined by him, at various times, since 1839. 

 He mentions particularly the rock from the Des Chutes River, collected by Fre- 

 mont ; also trachytic tufa, with organic remains, from Honduras ; trachytic 

 tufa from the volcano Maibu, in Chile ; the mud-ejections (?) of the volcanoes 

 near Quito ; the ejections (?) of the volcano Imbabaru, as well as those from 

 the island of Guadaloupe. 



In regard to the Des Chutes River deposit, it may be incidentally remarked 

 that the eminent microscopist seems to assign to it a much greater geological 

 age than it really deserves ; it is, unquestionably, as recent as the latter part of 

 the Pliocene. 



It would appear from what Ehrenberg has published, that he considers this 

 occurrence of organic forms, in connection with reputed volcanic masses, to be 

 something extremely difficult to explain, as indeed it is, if we adopt the view 

 taken by him, namely, that these so-called tufaceous materials are the direct 

 products of volcanic action ; that is to say, that they have been ejected from. 

 craters, either in the form of showers of ashes or of mud out-flows. It would be, 

 indeed, to my comprehension, something entirely inexplicable, that such vast 

 masses of matter, made up to a large extent of organic forms, should be poured, 

 forth from the interior of the earth. This would be the case, as it appears to 

 me, no matter what theory of volcanic action one might choose to adopt ; 

 since, whatever, may be the cause, no one will deny that a high temperature is, 

 at least, one of the results. That Ehrenberg really considers these infusorial 



* See Monatsbericht der Kbn. Preuss. Akaii. zu Berlin, 1866, page 158. 



