Ehrenberg on Infusoria in Igneous Rocks. 407 



fragmentary state ; and in the pumiceous conglomerate, or, as it is 

 called, the sandstone of Engers, it is not the grey interstratified mass, 

 but the white pumice-like nucleus of the conglomerate, which also 

 here and there contains similar organic bodies though in a fragmen- 

 tary condition. Many of these in the regular volcanic tuif forma- 

 tions appear to have become quite unrecognisable ; but amongst the 

 mass some may often be found which enable us to determine both 

 the genus and species of the little animalcule of which they are the 

 remains. 



In most of these volcanic tuffs one may often perceive, by using 

 transmitted light, green, brown or white crystals, of which the green 

 are for the most part columnar, oblique-rhomboidal, acutely-pointed 

 prisms, appearing black with reflected light, being in all probability 

 crystals of augite, while the obtuse brown crystals are more likely to 

 be hornblende. Many of the tuffs contain great quantities of exceed- 

 ingly small white transparent crystals in which sometimes there may 

 be distinctly traced the rhombic-dodecahedral form, and these no 

 doubt are sodalite, or perhaps occasionally leucite. 



2. The masses thus characterized appear to be, as they have al- 

 ways been considered, of volcanic origin. The numerous small crystals 

 of augite which make up so large a part — often at least one-half of 

 the whole mass — and those white kernels and particles of sodalite and 

 leucite visible to the naked eye, have hitherto been considered as the 

 result of the action of heat, since we are not aware of the possibility 

 of such forms of the mineral being producible by aqueous action. 

 The application of the microscope to this subject, showing that the 

 condition of the siliceous infusorial cases is such as would be the 

 effect of exposure to very high temperature, has fully confirmed 

 this view. 



3. The stratified mass at Hochsimmer can no longer be considered 

 as an aqueous formation, fused into a mass by volcanic action imme- 

 diately after its deposit ; since the condition of the different strata 

 is not such as would be produced by such means. Several experi- 

 ments seem to prove that the most perfect fusion has been effected in 

 portions which are by no means the lowest in position. 



4. The tuff of Hochsimmer could not, it would seem, have been 

 formed under water, because, the materials of the strata are not 



3 G 



