324 Ernest W. Skeats : 



rocks are rather spai'ingly represented. Dr. Howitt has dis- 

 cussed so fully most of the characters of the igneous rocks that 

 it is not necessary to do more than refer briefly to them, except 

 the more altered rocks, in relation to the question of the origin 

 of the silicification of the Heathcote rocks. 



Intrusive Rocks. — Dr. Howitt has described some of the 

 diabases as intrusive rocks, and among the small intrusions in 

 the form of bosses are the Diorite Knob at S. Heathcote, and 

 another similar mass just west of S. Heathcote station. An- 

 other rook from about ^ mile N. of the Selwynite outcrop, which 

 I have examined (No. 630), is holocrystalline, and is clearly an 

 intrusive diabase. They show distinct petrological characters 

 from the diabase series, as Dr. Howitt has pointed out, yet they 

 are almost certainly genetically related to the diabase magma, 

 and represent rather later and somewhat less basic intrusions of 

 the magma. 



Basic Lavas. — Rocks of this character appear to be sparsely 

 represented in the southern part of the area examined, but have 

 been met with in several areas between the Selwynite outcrop 

 and Lady's Pass. Some of the diabase rocks just south of Lady's 

 Pass appear to be lavas, and two other rocks may be specifically 

 referred to. 



Opposite the Junction Hotel, about a mile S. of Lady's Pass, 

 is a massive outcrop of a compact diabase. Under the micro- 

 scojje (Section 601) the rock is seen to be distinctly porphyritic, 

 comparatively freish phenocrysts of plagioclase, and chloritise-d 

 pseudomorphs after hornblende or augite are set in a fine felted 

 groundmass, which has been recrystallised as a mixture of 

 needle-shaped actinolites and a colourless base, possibly felspar 

 and quartz. Associated with the chloritic pseudomorphs are 

 secondary crystals of epidote. Li its altered condition the 

 precise nature of the rock is difficult to determine ; it might be 

 an intrusive or an effusive rock. From its field characters I am 

 inclined to regard it as a porphyritic lava. Another rock of less 

 equivocal character was examined in a paddock about 300 yards 

 W. of the Murray road, and about lAm N. of the Selwynite out- 

 crop, in allotment AG, Knowsley East. The diabase rocks here 

 form a ridge, and are considerably altered to siliceous and 

 calcareous diabases. 



