326 Ernest W. Skeats : 



Tuffs. — Under this description I place the platy diabase of 

 Red Hill, described by Dr. Howitt as a sheared diabase, and 

 similar rocks near Photograph Knob, just south of the cherts of 

 Lady's Pass, below the cutting in Ordovician on the Derrinal 

 road about \ mile N. of the Murray road junction, the diabase 

 from allotment 3q, Knowsley East, and from the isolated diabase 

 mass in E. Tranter's allotment M. of W., Knowsley East. Some 

 of the highly altered diabase rocks to be described later are also 

 quite possibly fragmental in origin. Owing to the alteration and 

 foliation of these rocks, in no case is the characteristic structure 

 of the groundmass of a normal tulf preserved. Both in the dia- 

 base of lied Hill and in the rock in the gully S. of Photograph 

 Knob the fragmental character can be seen in the field, and in 

 hand specimens, and a passage from these intn finer-grained 

 rocks, presumably volcanic ashes, is to be obser\'ed. The inclu- 

 sion of coarser typeis like the agglomerate (No. 576), described 

 above in the finer platy diabase of Red Hill, is significant, and is 

 of assistance in determining the original character of these 

 altered rocks. Tbe rock from the stream bed S. of Photograph 

 Knob shows in section (No. 582) parallel development of chlorite 

 and secondary quartz and felspars, and some magnitite. Irre- 

 gular lighter coloured areas may represent fragments of a rock of 

 different character. »The dense, fine-grained diabasio rocks from 

 the paddock \ mile S. of Photograph Knob (No. 597), and from 

 the area previously mapped as Ordovicia.n, just N. of the felspar 

 porphyrite (No. 614), have been previously referred to, and their 

 resemblance to a fine indurated bluish diabase at the S. end of 

 Red Hill (No. 633). From their association with rocks whose 

 fragmental character is clearly visible, I regard these types as 

 probably voloa.nic ashes, which by alteration and subsequent pres- 

 sure have been indurated and have developed a marked folia- 

 tion. Their character is in striking contrast to the diabases 

 which can be shown to have been lava flows and intrusions, and 

 which appear to have undei'gone the same mineralogical changes 

 as the foliated diabases. 



A rock whose fragmental cliaracter is cleaily manifest (No. 583) 

 (Pi. XIV., Fig. 4) is the type i-epresented in allotment 3(}, Knowsley 

 East, where, according to the Quarter Sheet and to Prof. 

 Gregory, no diabase occurs. Under the microscope the rock is 



