644 Granite at Mounts Adam and Eve. 



Petrography of the Limestones. 



The white limestone at a distance from the granite shows little 

 of interest. It is a coarsely crystalline mass of calcite individuals 

 with an occasional scale of graphite. Scattered six-sided crystals 

 of phlogopite are now and then present. They are colorless to very 

 faint brown, have a small angle of the optic axes, perhaps 5°, and 

 show the normal properties of mica of the second order, as regards 

 the percussion figure. The streaks of chondrodite that also appear 

 lead one always to suspect the proximity of granite, even though it 

 may not outcrop. Chondrodite appears in or near the undoubted 

 contacts in its best development. 



The blue limestone is much finer in crystallization, but is made 

 up of small calcite crystals, and near the borders of the white lime- 

 stone it becomes itself graphitic, and in fact shows all intermediate 

 stages of transition. 



The Contacts. 



The most interesting features of the exposures are to be found 

 along the contacts of the granite and white limestone. In several 

 places we found these in place, and in many other instances traced 

 either the white limestone or the granite to a point where they could 

 not have been over a few feet apart. Interesting and marked changes 

 manifest themselves in both granite and limestone. In general it 

 ma}^ be said that either the former becomes an aggregate of light 

 green monoclinic pyroxene and scapolite, or we find a granite-like 

 zone formed by these two. With them titanite is quite invari- 

 able. This association was so often found that it justifies speak- 

 ing of the ''scapolite zone." Whether this zone is to be considered 

 a contact phase of the limestone or of the granite may be a ques- 

 tion, but the specimens were in most cases gathered as granite and 

 only recognized in the thin sections. Where, however, the scapo- 

 lite is sufficiently coarse, it looks, to use the felicitous comparison 

 of the Norwegian geologists, like "w^et snow." The limestone 

 near the contacts becomes charged with silicates, either in bunches 

 and irregular masses, or else in general dissemination. These 

 masses are chiefly brownish-green hornblende of a peculiar tint, 

 dark brown biotite or phlogopite (the distinction between these is 

 obscure), light green pyroxene, titanite, calcite, pyrite, and some 



