320 Ernest W. Skeah : 



to a black chert. Closer investigation, however, showed that on 

 the E. and N.E. sides, especially in a shallow railway cutting S. 

 of Gate 51, less silioified jwrtions of the same bedded series are 

 represented, and pass gradually into a bedded fragmental diar 

 basio rock, apparently a bedded diabase tuff. The evidence seems 

 clear, then, that here the bedded black cherts, with associated 

 ironstones, are simj^ly silicified, probably submarine, basic tuffs, 

 or rocks made up of diabase fragments. A few hundred yards 

 beyond this hill the Ordovician diabase junction crosses the 

 Derrinal road near a road cutting. The Ordovicians are soft 

 brown shales containing numerous Magnesite concretions, strike 

 N. 10 deg. W. about, and are nearly vertical. On the east side 

 of the road cutting a feav yards from the road, silicified shale waa 

 seen, and in the bed ' of the Mt. Ida Creek is an outcrop of a 

 dense silicious rock, with Pyrite abundantly scattered through 

 it. The rock looks at first like a quartzite, but under the micro- 

 scope is clearly seen to be an igneous rock, consisting mainly 

 of lath-shaped plagioolase, chloritised biotite and some Pyrite 

 (Sec. 648). A few yards down stream the diabase was seen in 

 situ, and is partly fragmental in character. Massive silicified 

 diabase was seen a little N.E. of the road cutting, and again 

 in a cliff section on the E. bank of the Mt. Ida Creek, north of 

 the outcrop of silicious diabase. I have also examined the 

 junction between diabase and Ox'dovician, at several points fur- 

 ther north, notably W. and S.W. of the Selwynite outcrop, north 

 of paddock A^, Knowsley East, near the southern end of the 

 Dinesus beds, in paddocks .'5 and 3q, and also in paddocks 3m 

 and 3j, Knowsley East. In all these places the Ordovician was 

 more or less cherty in character, and in several places the 

 Dinesus beds were distinctly cherty. Whatever explanation may 

 be offered of this feature. Dr. Howitt's claim for the marginal 

 alteration of the Ordovician near the diabase contact is one 

 that can be ge^nerally substantiated in the field. It should be 

 noticed that on Lidgey's may (Quarter Sheet No. 80), the diabase 

 is not represented as outcropping anywhere in allotments 3q 

 and 3m, Knowsley East, a gap of nearly a mile. In its place 

 a thin outcrop of " Metamorphio " rocks is sho\ni. Professor 

 Gregoi-y (op cit) refers to this locality as follows : — " Moreover 

 the metamorphic rocks occur in places where there are no 



