Speight. — The Tertiary Beds of the Trelissick Basin. 335 



south-east. The beds at this point have been subjected to a notable 

 twist, as has been mentioned previously, and the angle of dip rapidly in- 

 creases from 40° on the eastern side of Murderer's Creek to vertical with 

 a slight overturning at Parapet Rock, and continues so till the bed again 

 crosses Broken River at the upper limestone gorge. From just east of 

 Murderer's Creek to beyond Broken • River the limestones are involved 

 in the fault, and some of the underlying members have had their outcrops 

 suppressed (fig. 1). 



Throughout this portion of the line of outcrop the rock is of a hard 

 flaky nature, extensively jointed, a result due no doubt to the pressures 

 and dislocations to which it has been subjected. In places it is crystalline, 

 but traces of its coralline origin are visible throughout. It contains particles 

 of volcanic tuff, and at Parapet Rock itself there appears to be a distinct 

 layer of tuff, 4 ft. thick, dividing the stone into two layers, the lower 60 ft. 

 thick and the upper about 80 ft., the latter being less flaky, but breaking 

 into quadrangular blocks. It would therefore appear that there is the 

 division into two layers even in this part of the area, remote from the 

 centres of pronounced volcanic activity. 



In the area between Waterfall and Hog's Back Creeks the line of out- 

 crops forms a series of loops, resulting from the erosion of a succession of 

 anticlines and synclines. Continuing from Broken River crossing, it follows 

 the same direction as it has north of the river till it reaches Trout Creek, 

 when it swings round with a change of dip to the west, and forms the mass 

 of iSugarloaf Hill, whose bold escarpment fronts to the north-east. This 

 direction is continued across Waterfall Creek, the limestone itself forming 

 the lip of the fall from which the creek takes its name. After crossing 

 this creek the outcrop extends some distance up the steep slopes on the 

 north and then swings round, forming a syncline, the edges of the bed 

 cropping out on a series of low mounds in the direction of the Hog's Back 

 Creek. When this is reached another reversal occurs and the outcrop 

 follows back to the north, reaching Waterfall Creek once more and just 

 crossing it. At the southern end of this stretch the limestone is almost 

 vertical, and the upper edge of the beds forms a bold cliff along the base 

 of which the Hog's Back Creek flows — in fact, the limestone is probably 

 slightly overturned ; but to the north it slowly flattens out, preserving a 

 westerly dip, till in Waterfall Creek it is inclined at an angle of only 55°. 



Immediately north of this creek the line of outcrop turns back with a 

 reversal of dip, crosses the creek again, and the bed apparently peters out, 

 or is covered by surface accumulations and cannot be traced more than a 

 few chains south of the creek 



A small occurrence of limestone is found on the south side of the Hog's 

 Back Creek, in the vicinity of the greywacke slopes of the Craigieburn 

 Range, on the spur dividing that creek from the Thomas River ; but the 

 exposure is so small that it is impossible to determine its relations. It 

 may be a small block separated from the main limestone mass by faulting, 

 or be a part of a fold connected with the Hog's Back Ridge under the creek, 

 and overlain by more recent Tertiary beds. 



This limestone is generally hard, and somewhat jointed into flaky quad- 

 rangular blocks in its lower portions, but it varies much in character in its 

 various parts In many places the upper layers are distinctly crystalline. 

 Marshall gives the following microscopical description of this rock from a 

 specimen collected by the author : " Polyzoa are again the most frequent 

 organisms in this rock, though echinoderm plates are common. Foraminifera 



