GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 527 



The best exposure in whicli to study the segregation 

 veins is undoubtedly the Reservoir Quarry. Here may be 

 seen at a glance the two great segregation veins already 

 mentioned above (see Plates XXXV. and XXXVI.). They 

 lie about 4 m. (13 ft.) apart ; and they run parallel in a 

 remarkable degree with the junction surface of the pallio- 

 essexite and with the shales, following even minor undu- 

 lations of the junction, the uppermost at a depth of 13 m. 

 (45 ft.) below it. Where the junction turns sharply upwards 

 and vanishes in the present ground surface, near the north- 

 western end of the quarry, the great veins follow and also 

 are lost by denudation; so that in the middle of the quarry 

 the outcrops of these two veins upon the face are roughly 

 horizontal, whilst in the north-western part of the quarry 

 they dip to the south-east at 30° (see Plate XXXV). The 

 true dip of these great segregation sheets in the southern 

 half of the quarry may be ascertained by standing near the 

 face of quarry and looking to the south east. On the 

 southern wall of the quarry, although the rock is much 

 decomposed, the segregation sheets are clearly seen, dip- 

 ping at about 35° inwards, towards the face of the quarry 

 (see Plate XXXVI). Tlieir dip here is nearly east-north- 

 east, that is, directly towards the centre of the southern 

 part of the intrusion, as may be seen on consulting the 

 plan. The reason why the outcrops of the veins on the 

 face turn upwards and disappear in the northern half of 

 the quarry, is that these sheets no longer dip at right angles 

 to the face, but due east (magnetic). The sheets have in 

 the southern pavement of the intrusion, a quaquaversal 

 dip towards a centre of the intrusion. Bearing in mind 

 the close conformity of the outcrops of the sheets upon the 

 face with the overlying junction, it seems probable that 

 the sheets were everywhere parallel to the junction, hence 

 the upper surface of the intrusion near its periphery must 

 have had a quaquaversal inward dip of about 35°; which 



