34 Notes on the Diabase Rocks 



to Hie that the same contact continued well marked 

 throughout. There are always more or less of passage-beds. 

 The underlying felsitic beds are not, however, of the same 

 character in all places. Near the Murendel Mine the upper 

 bed of the lower series is distinctly composed of a mass of 

 felsitic fragments, among which felspar particles are recog- 

 nisable — therefore probably a tufa.* Some miles higher 

 up the river the passage- beds rest upon a true quartz 

 felsite. Intermediately, I found felsitic rocks of both 

 kinds, and also of varieties of which I could not say, 

 with any feeling of certainty whether they were originally 

 fragmental or not. I have said that in tracing the course of 

 the Murendel River upwards, it is also possible to trace 

 with more or less distinctness the course of the felsitic beds 

 on which the Upper Buchan beds (Buchan limestones) rest. 

 It is seen that the latter have not only a general westerly 

 dip, but also a marked undulation along the strike, thereby 

 producing a number of secondary clips at right angles to the 

 main dip, but of limited area and extent, forming a series of 

 synclinals and anticlinals. The felsitic rocks, the passage- 

 beds, and the lower of the marine limestones, therefore, 

 alternately rise and fall below the level of the stream, which 

 may be broadly stated to flow along the contact of the upper 

 and lower beds. Thus there are usually on the western side 

 high and precipitous limestone cliffs, showing at their base 

 traces of the felsitic beds ; while on the eastern side are 

 almost wholly rugged hills of harsh and massive felsites. 



On approaching that part of the valley known as the 

 Pinnacles, where the river has formed a subterranean 

 passage through the limestone hills, and only flows over the 

 surface during floods, the felsites no longer have the well- 

 marked, bedded, and fragmental character of those nearer 

 the mine, but are to all appearance characteristic examples 

 of a reddish or salmon-coloured quartz felsite. 



In certain places I found it to have a ground-mass 

 resembling a reddish felsite, studded with rather perfect 

 dihexahedra of quartz. The rocks are then traversed by a 

 few joints, dipping S. 70° W. at about 26°. The river has 

 eroded during floods a channel in these hard and massive 

 rocks, with smooth and almost polished sides, and with many 

 huge " giant kettles." This is very favourable for the study 



* Locally where the Diabase rocks occur the fragmental beds are either 

 composed wholly of their fragments or of these mixed with felsitic materials. 



