344 TtHEat serpentink belt of new south walks, vii., 



thus through Portious 36 and 37, at the southern end of which 

 it is cut oif by a fault, which throws it eight hundred yards to 

 the east. Thence it continues for a mile further, exhibiting 

 some very interesting features described below (p. 345). This 

 belt of keratophyre forms the western margin of the Transitional 

 Zone; except where jasperised, the rocks to the west of it ob- 

 viously belong to the Tam worth Series. In Portion 52, a small 

 amount of such jasperised rock occurs, the relations of which 

 have been obscured through the ploughing of the land. More 

 distinct is the small mass of jasper in Portion 35, in contact 

 with a keratophyre rather rich in magnetite. 



The main mass of the keratophyre is a rock of fine to medium 

 grain-size, consisting chiefly of albite, a few phenocrysts lying in 

 a trachytic or spongy base, dotted with finely crystalline mag- 

 netite. A little quartz is present in the base together with some 

 chlorite. Occasionally, the rock is quite coarseh^ crystalline, 

 and contains a little augite, approaching the character of albitic 

 quartz-dolerite (1414). 



Along the eastern margin of this intrusion in Portion 36, the 

 rock is distinctly brecciated, this facies passing imperceptibly 

 into the massive rock. In microscopic examination, it has the 

 character of a flow-breccia, and sometimes appears to have been 

 originally more or less glassy. Fragments of albite occur with 

 very irregular outline and often slight strain-structure, also 

 irregular fragments of quartz and small grains of uralitised 

 augite, lying in a cryptocrystalline base (1411). In some speci- 

 mens, the matrix is the predominant portion; in others, the 

 larger fragments of crystals, evidently derived from a shattered 

 dolerite and quartz-keratophyre, form the dominant feature of 

 the rock. With such large fragments of single crystals may be 

 associated chips broken from a minutely trachytic keratophyre 

 (1406), such as are so abundant in the keratophyre-breccias of 

 Pipeclay Creek (5, pp. 15 1-156). 



In places, the keratophyre becomes enriched in magnetite, and 

 a dark magnetite-keratophyre occurs by the jasper in Portion 

 35, as noted above, and in the south of Portion 37. The best 

 examples of magnetite-keratophyre, however, are to be found in 



