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exhibits a variegated mass of pale green serpentine and a nearly colourless 

 substance intimately blended together (see figure) : imbedded in this matrix 

 there are numerous pseudomorphs after olivine, and irregular plates of unaltered 

 augite, together with minute grains of magnetite, scattered here and therethrough 

 the mass. The pseudomorphs after olivine .are of two kinds, consisting either 

 of serpentine or the white colourless substance just mentioned ; both are 

 highly characteristic ; the crystalline forms are perfectly preserved, and they 

 are traversed by veins representing the original cracks so generally found in 

 this mineral. Although the groundmass of the rock exhibits a confused 

 appearance both in ordinary and polarized light, we are fortunately not left in 

 doubt as to the nature of at least one of the original constituents. The augite 

 frequently encloses highly characteristic pseudomorphs after felspar ; some 

 are completely enclosed, while others are only partially embedded in it. 



In many cases the unaltered augite has preserved in the most perfect 

 manner the sharp edges and angles of the felspar prisms ; and whenever the 

 latter project from the augite, it may be readily seen that both the enclosed 

 and outlying portions have been converted into precisely the same serpen- 

 tinous substance as that forming the groundmass. It should also be noted that, 

 in the case of partially enclosed prisms, only those sides or ends which have 

 impressed their shape on the augite exhibit a crystalline form, the outstanding 

 portion being quite undistinguishable from the surrounding mass." Mr. 

 A i, i, POUT regards the rock as furnishing an illustration of the partial serpen- 

 tinisation of an olivine -dolerite. The extraordinary abundance of the olivine, 

 as evidenced by the numerous pseudomorphs, and the comparatively small 

 amount of felspar which can have been present, are sufficient to place the 

 original rock in the picrite group. "Professor ROSEN BUSCH refers to a picrite 

 from Liskeard in his Mikroskopische Physiographic der massigen Gesteine 

 (1st Edition p. 530), and there can be no doubt from his description that he is 

 speaking of the rock now under consideration. He mentions the occurrence 

 of minute colourless microlites in the sepentine after olivine, and doubtfully 

 refers them to a grammatite-like amphibole. In some of the slides examined 

 by the present writer, cross sections of these microlites give the outline of a 

 hornblende prism, and leave no doubt as to the correctness of Professor 

 ROSENBUSCH'S suggestion. Here then we have another illustration of the 

 formation of secondary hornblende in connection with the serpentinising 

 process. 



One of the most interesting points about this rock is the evidence it 

 affords of the alteration of felspar into a substance which blends in the most 

 intimate manner with the serpentine derived from olivine. We have no direct 

 evidence of the nature of this, but it is probably the substance which has 

 frequently been termed pseudophite ; that is a substance which retains the 

 original alumina of the felspar in combination with magnesia and water ; the 

 lime and alkalies having been removed. It is instructive to notice that in 

 this rock the felspar and olivine have both been attacked and completely 

 destroyed, whereas the augite is frequently preserved. 



Angletea. Several patches of serpentine are represented on the one-inch 

 geological map of Anglesea. These patches are very briefly referred to in 



