. Journal and proceedings of the Royal Society of New South Wales . ixty-five feet (in the Reservoir Quarry). As com-pared with the original undifferentiated magma it has beenimpoverished by the concentration of olivine in the pallio-essexite, by the relative concentration of felspars andbiotite in the felspathic zone, and also by the concentrationof alkaline minerals (albite and egerine) in the segregationveins. To what extent it differs from the original magmaas a result of these impoverishments it is, in the absenceof any positive knowledge as to its thickness, impossible tosay. It is proba
. Journal and proceedings of the Royal Society of New South Wales . ixty-five feet (in the Reservoir Quarry). As com-pared with the original undifferentiated magma it has beenimpoverished by the concentration of olivine in the pallio-essexite, by the relative concentration of felspars andbiotite in the felspathic zone, and also by the concentrationof alkaline minerals (albite and egerine) in the segregationveins. To what extent it differs from the original magmaas a result of these impoverishments it is, in the absenceof any positive knowledge as to its thickness, impossible tosay. It is probable, however, as stated above, that therapidly cooled pallio-essexite, after deducting the excess ofminerals resulting from fractional crystallisation, mostnearly represents the original composition of the The Segregation Veins. The nature and distribution of the segregation veins hasbeen fully described in our previous paper (p. 526). Thetwo large veins therein described, occur in the felspathiczone of the essexite, and one of them is shown in figure Pallio-Essexite. Essexite. :*j UjjpciSc^regatioT) Vein|£^ Essexite. Fig. 1.—Sketch of part of the face of the Reservoir (old) Quarry. DIFFERENTIATION PHENOMENA OF THE PROSPECT INTRUSION. 131 It will be seen that it parallels in a remarkable way theupper surface of the intrusion, and is about nine metresbelow the junction of the intrusion with the shales; theone not shown is parallel to it, and about four metresbelow it. These two veins have a thickness varying from15 cm. up to 120 cm., and contain two distinct rock types,which we have called essexo-pegmatite and essexo-apliterespectively. The relation of these rocks to one another,and to the essexite proper is shown in figure 2.
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