104 



lenticles and bands of a peculiar pegmatite. As no 

 variety of pegmatite, described in Rosenbusch's "Mikro- 

 scopische Physiographic der Massigen Gesteine" (1908), ap- 

 pears to resemble this rock to any extent, I have ventured to 

 suggest for it the name Yatalife, from its occurrence in the 

 Hundred of Yatala, and to describe it hereunder as a new- 

 variety of j^egmatite. It consists of a coarse-grained aggre- 

 gate of actinolite (after diopside), titaniferous magnetite, 

 albite, sphene, apatite, and quartz. 



This intrusion appears on the road between Houghton 

 and Ingle wood, and continues thence for a couple of 

 hundred yards beyond the Inglewood Hotel. It runs north- 

 wards from this line till it is cut out by the Cambrian series 

 along the Little Para River. It runs southwards from 

 Houghton with a slightly easterly trend, crossing the Torrens 

 River about a mile above its junction with Kangaroo Creek, 

 and just south of the river it disappears beneath the Cam- 

 brian basal beds. It is thus over four miles in length, with 

 an average width of perhaps half a mile. It sends out a 

 vein which leaves the main intrusion about a mile south of 

 Inglewood, and ends near the main Gumeracha Road after 

 crossing the Little Para. Isolated areas of the rock occur 

 both to the east and west of the main intrusion, and these 

 may present rather different though related rock types. 



Besides the yatalite pegmatite a little normal granite 

 pegmatite is to be found, especially to the west of the in- 

 trusion, as, for instance, in the quarry by Houghton school- 

 house. This has a strongly gneissic appearance. 



Along the western side of the intrusion are certain highly- 

 altered rocks, probably a result of contact alteration pro- 

 duced by the intrusion. These apparent schists are pro- 

 bably altered syenites. The line of demarcation between 

 these and the true sedimentary schists is by no means clear. 



As to the age of these schists there is little evidence to 

 offer. They are not here very highly metamorphosed, and 

 are thus to be referred to the Algonkian period rather than 

 to the Archaean. Dr. Woolnough has proposed the name Baros- 

 sian for the augen gneisses and related rocks of the Barossa 

 Ranges, '^^ and as will be shown later the Houghton schists 

 are petrologically closely related to these. It seems, then, 

 quite admissible to apply the term Barossian as indicating 

 vaguely an Algonkian period to the rocks of Houghton and 

 the other areas of the same type. 



The age of the intrusion is also Algonkian. It is, of 

 course, quite impossible to fix with any certainty its date in 



(5) Trans. Roy. See, S.A., 1908, p. 132. 



