DIFFERENTIATION PHENOMENA OF THE PROSPECT INTRUSION. 



131 



It will be seen that it parallels in a remarkable way the 

 upper surface of the intrusion, and is about nine metres 

 below the junction of the intrusion with the shales; the 

 one not shown is parallel to it, and about four metres 

 below it. These two veins have a thickness varying from 

 15 cm. up to 120 cm., and contain two distinct rock types, 

 which we have called essexo-pegmatite and essexo-aplite 

 respectively. The relation of these rocks to one another, 

 and to the essexite proper is shown in figure 2. 



Fig. 2. — Sketch of part of one of the larger Segregation Veins. 



A Essexite (dolerite); B Fine essexo-pegmatite; C Coarse essexo- 

 pegmatite ; D Fine aplite ; E Coarse aplite. 



