346 THE MELILITE BASALT OF SPIEGEL RIVER 



for considering the whole group as belonging to one 

 period of volcanic activity will be given, together with 

 other points of general interest. 



On the farm Spiegel Eiver in the Eiversdale Division 

 there is a most remarkable mass of melilite-basalt (al- 

 noite) exposed at the top of a hill composed of conglo- 

 merates and sandy beds belonging to the Uitenhage 

 series. 



The area occupied by the alnoite, as shown by arti- 

 ficial cuttings, is somewhat pear-shaped and measures 

 300 yards in a north-east and south-west direction and 

 220 yards across the widest part near the south-west 

 end, but the outcrops are only seen over a small area. 

 The junction with the surrounding beds has not been 

 exposed. 



The grey-black igneous rock is in places roughly 

 columnar, but the columns are very feebly developed ; 

 they slant towards the east. The only feasible explana- 

 tion of the occurrence is that the melilite-basalt fills a 

 volcanic neck. The want of good exposures and the 

 crumbly nature of the conglomerates prevent the ob- 

 servation of the dip of these beds at the contact. The 

 beds are seen at several places within 200 to 300 yards of 

 the vent, but they present no points of difference from 

 their nature at a greater distance from the spot. No 

 other neck or intrusion has yet been found in the 

 Uitenhage beds, and till lately no other occurrence of 

 melilite-basalt had been observed in South Africa. The 

 rock is composed of a ground mass of glass in which 

 there are minute crystals of perofskite and magnetite, 

 irregular grains of augite, immense numbers of melilite 



