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pliosphatization, dolomitization, or ferric oxidation of the 

 limestones. The following localities and geological horizons 

 give illustrations of our subject. 



MOUNT REMARKABLE (Autoclastic). 



This truly ''remarkable" mount, situated in the southern 

 Flinders Ranges, 150 miles north of Adelaide, forms a very- 

 prominent horst with quartzites, of Lower Cambrian age, as 

 the chief lithological feature. On its eastern side the mount 

 rises abruptly from the plain to a height of over 2,000 feet, 

 and has a fault-displacement on that side of several thousands 

 of feet. The Brighton Limestone series make prominent 

 features on both the eastern and western sides of the mount, 

 the dip is anticlinal with a high pitch, to vertical, on the 

 eastern side of the mountain. Autoclastic phenomena, on a 

 very extensive scale, occur on the south-eastern, southern, 

 and south-western sides of the mount. The brecciation, whilst 

 associated with several important fault-plane®, is something 

 more than an ordinary fault-breccia. The shatter-zone on the 

 south-eastern side of the mount is three miles long, and, 

 near Melrose, is half-a-mile wide. It extends from the level 

 of the Mount Remarkable Creek (a little higher up the stream 

 than Melrose) to a height of 600 feet up the mountain side, 

 at the ''Cat Rocks,'' nearly opposite Melrose. The "shatter"' 

 occurs on both sides of the great fault- displacement, and 

 includes, (a) the impure siliceous limestones of the Brighton 

 series underlying the true limestone; (h) thick. Lower 

 Cambrian, dark-coloured shales (or slates), and (c) the 

 adjoining portions of the thick quartzite on the one side, and,, 

 to some extent, the thick limestone on the other. 



The brecciated beds are in the creek at the southern end 

 of the mount, with the "Gibraltar Rock" (in the form of a 

 high fault-scarp of the quartzite) on the northern side, and 

 a range of brecciated rock on the southern side of the stream, 

 which continues round to the south-western angle. 



Over the greater part of this broken country the original 

 planes of stratification are entirely destroyed, and angular and 

 rounded fragments of the associated beds are irregularly 

 distributed through a mylonitic base. In some instances the 

 original lamination of the bedding can be recognized in the 

 included fragments. It forms an example of autoclastic action 

 of a peculiar kind. It did not develop along a thrust-plane of 

 low angle, as commonly is the case in crush-conglomerates, 

 and it is also different from what is ordinarily known as a 

 fault-breccia. It might be described as a long and wide^ 

 segment (or segments) of the earth's crust, that has slipped 



