71 



stone is exposed; it has a laminated structure and is under- 

 going change to manganic and ferric oxides: dipS. 10° W. 

 at 30°. . ■ 



Tlie Mount Lyall Range extends from the old station, 

 in a north-easterly direction, for a distance of about 3 miles. 

 At Mount Lyall (fig. 2) it forms a sharp angle with a range 

 that comes down from the north. At the angle is a prominent 

 hill, about 150 ft. in height, which shows a scarp face to the 

 south-east. This hill is a solid mass of limestone, brownish 

 in colour, dolomitic, and very compact. The section repre- 

 sents the lower beds of the Archaeocyathina© series. These 

 beds follow the strike of the northern range of hills, but they 

 appear to run out to the northward. It is probable that 

 the scarp face of the hill. is a fault plane. Tli'e hill just 

 mentioned has a dip at the summit N. 10^° E. at 15°. From 

 the top of the hill it could be seen that the beds on the north 



MZyccll 



Fig. 2. Geological Section of Mount Lyall. 



side of Mount Lyall were much disturbed, dipping at various 

 angles both to the Mount Lyall Range and also to one another. 



The peak of Mount Lyall dips N.W. at 60°. The north- 

 eastern end of the range is broken by ( ?) two faults. Mount 

 Lyall peak dips as above, then on the eastern side the dip 

 somewhat suddenly changes to nearly horizontal. After a few 

 hundred yards at this level there is a sudden break, M^hen the 

 purple shales, much crumpled, are thrown down to the face 

 of the quartzites with a dip N. 20° W. at 35°. A crush-zone 

 occupies the fault area for a thickness of about 9 yards. A 

 series of underlying dolomitic limestones, purple shales, and 

 quartzites follow with a rising dip, going east, to 50° (see 

 fig. 2). Just round the northern end of the range there is 

 an oblong dyke of intrusive rock. On the eastern side of 

 the dyke there is a crush-rock, composed of flaggy shales, of 

 considerable extent. This is probably on the line of fault, 

 noted above, that cuts through the north-eastern part of the 

 range. 



There are low exposures of the Archaeocyathinae lime- 

 stone, in the form of a fragment (probably limited by two 



