28 PROF. T. G. BONNEY ON THE [Feb. 1 896, 



relation of these two rocks by one of four hypotheses : (a) that the 

 two rocks have been brought together by faults ; (6) that the two 

 have been folded together ; (c) that the two have flowed together ; 

 (d) that the serpentine is intrusive in the granulitic rock. 1 



As the relations of the two rocks have been described in former 

 papers, I shall not repeat what is already in print, but content 

 myself with remarking that though I have again examined all these 

 cases, I find no reason for altering my statements, and with describing 

 very briefly a few other instances. As a preliminary, I venture 

 to remind the reader that the granulitic rock commonly occurs as 

 blocks, which sometimes appear to be completely included in the 

 serpentine, but at others may be either projecting ridges or crags 

 attached to much larger masses below or behind the visible surface. 

 Where these exhibit a definite structure, this seems more or less to 

 determine their outline, so that well-banded varieties are often fairly 

 rectangular in shape ; but as such a structure is not always present, 

 considerable variety of form is possible. Though small slips and 

 displacements are common in the serpentine, the faces of these 

 blocks do not appear, as a rule, to correspond with faults ; moreover, 

 the two rocks occasionally, though not commonly, are welded 

 together — in other words, the relations of the granulitic rock and 

 the serpentine appear to me, as a rule, incompatible with the first 

 or the second hypothesis. As for the third, it may be understood to 

 mean either that the two rocks have been simultaneously emitted as 

 parts of a magma already separated in accordance with Soret's or 

 some other principle, or that the one material has been injected into 

 the other, and has so completely softened it, if it were already 

 solid, that the two have subsequently flowed on together. Now, 

 the granulitic mass itself exhibits irregularities in structure and 

 variations between the extremes of mineral composition, which 

 accord well enough with the one or the other of these interpreta- 

 tions ; but between it and the serpentine no transitional condition 

 can be found, neither does it occur in lenticular or streak-like bands, 

 such as the third hypothesis would lead us to expect, but in blocks ; 

 while the fourth hypothesis, as I trust will be perceived from the 

 evidence which I am about to quote, accords better with the facts. 



Time, however, may be saved by noticing at the outset a general 

 objection which might not unreasonably be raised, namely that, if the 

 serpentine be intrusive in the granulite, its relations to the latter 

 are rather unusual. It has formed neither dykes nor branching 

 veins in the * granulite/ nor has it shattered that rock and caught 

 up numerous small fragments. Yet all these are done by granite, 

 diorite, gabbro, and other deep-seated rocks, as well as by their 

 more compact representatives. The serpentine adopts the form, 

 as those holocrystalline rocks often do, of irregularly-rounded 

 bosses or somewhat elongated tongues, but it is not connected, as 

 they very commonly are, with peripheral dykes and veins. This, 

 however, appears to be the usual habit of peridotites and serpentines. 



1 I exclude that already mentioned, namely, that the granulite is the intruder, 

 because, in the cases which I am about to mention, I cannot conceive the possi- 

 bility of its being seriously entertained 



