322 Scientific Intelligence. 



doubt that it will be argued that changes that occur in such 

 small specimens should not be used as a guide to what occurs 

 in large masses. To this it may be answered that the greater 

 number of chemical phenomena that occur in the mineral world 

 can be studied on the smallest scale in the laboratory. But 

 beyond this these very same metamorphic changes may be traced 

 on a much grander scale amongst the ejected blocks of Monte 

 Soraraa, and I propose to confirm and extend these few notes in 

 another paper on the massive limestones and their derivatives. 



" Further, when we extend our investigations to the contact 

 phenomena of such a region as the Tyrol, which are probably of 

 less importance than what is really going on beneath Vesuvius, 

 and from thence pass to areas of regional metamorphism, we are 

 struck by the great similarity in the changes that have taken 

 place. It must, however, be borne in mind that three important 

 factors enter into the question, namely, the composition of the 

 rock to be acted upon, that of the magma acting, and the time, 

 circulation, and quantity of the latter. And equally imperative 

 is it to remember that such rocks which reach the surface by 

 denudation of the overlying materials have been exposed to so 

 many fresh changes as sometimes to be no longer recognizable. 



"The changes that take place in an impure limestone seem to 

 be, in the first place, the carbonization of the bituminous contents 

 with the conversion of them into graphite. Almost coincidentally 

 re-crystallization seems to have taken place, for what was an ex- 

 tremely fine-grained rock begins to approach the saccharoidal 

 structure. This re-arrangement or re-crystallization seems to 

 have occurred without the rock having become fused, or even 

 pasty, since the most delicate stratification, banding, faulting, 

 and contortion structure is preserved. At this stage a few grains 

 of peridote begin. to make their appearance, chiefly as inclusions 

 within the calcite crystals. The next process is the destruction 

 of the graphite, and in some cases its apparent replacement by 

 peridote, as in specimen No. 200. In the early stages of carbon- 

 ization the graphite exists between the grains, but later gets 

 enclosed within them, as if they had undergone fusion. With 

 the disappearance of the graphite, what remains is a more or less 

 coarse-grained, dazzling white marble. This saccharoidal marble, 

 containing more or less white peridote, passes somewhat abruptly 

 into a mass of peridote and white pyroxene, wollastonite, or bio- 

 tite. Why, sometimes it is one or sometimes another mineral 

 that borders on the white marble, I feel inclined to attribute to 

 the impurities in the original limestone in the absence of alumina, 

 with a supply, though limited, of silica, with much lime and mag- 

 nesia, so that either fosterite or monticellite may result, and, if 

 much iron, even true olivine may separate out. If only silica and 

 lime are present, then we must look for wollastonite. Likewise, 

 the presence of fluorine may determine the crystallization of 

 humite instead of peridote. In the same way we understand 

 how the other minerals may separate. Now, in a stratified lime- 



