THE VICTORIAN NATURALIST. 47 



no time was spent in looking for them, as when they do occur in 

 our Upper Silurians they are usually confined to thin bands inter- 

 bedded with thick series of unfossiliferous rocks. The evidence 

 of the fossils obtained from similar-looking rocks elsewhere about 

 Melbourne has, however, enabled their age to be determined. 

 In consequence of the absence of fossils, we spent a considerable 

 time in examining and discussing the effects of rock folding as 

 shown in the cutting. It is always well to begin at the very 

 beginning, and to make sure of our foundation before erecting 

 the superstructure, so it may be pointed out that the rocks in 

 question were laid down as a series of sheets at the bottom of the 

 sea. That it was a salt, and not a fresh water deposit, we learn 

 from the nature of the fossils before alluded to. On first entering 

 the cutting, it was noticed that thin beds of sandstone alternated 

 with thin beds of shale. This, of course, showed that the condi- 

 tions of deposition were constantly changing, that the ocean 

 currents were at one time sufficiently rapid to roll along grains of 

 sand and spread them evenly on the bottom, and at the same 

 time too strong to allow the fine mud to settle to any great extent; 

 while at another period of deposition they were so feeble that 

 they could not bring the sand grains from the wasting land 

 surfaces, and the suspended mud slowly sank to the bottom, 

 which it covered with a series of thin uniform sheets. 



The numerous spangles of mica in the rock may have been 

 derived from older rocks, which supplied the material of their 

 mass, or may have been subsequently formed in the rock itself. 

 The rocks as we see them to-day are strangely twisted and 

 crumpled. The beds in which they were laid down no longer 

 preserve their horizontal position but are inclined at various 

 angles to the horizon, and are in places broken and faulted 

 where the strain caused by the folding grew too strong for them 

 to withstand. Several of these faultings were noticed, and it was 

 seen that in many cases the walls of the faults were smoothed and 

 scratched by the rock movement which had taken place. The 

 direction of the scratchings, or " slickensides," as they are called, 

 was not vertical but inclined downwards towards the south and 

 up towards the north. This showed that the movement had not 

 taken place vertically but in a north and south direction, with, 

 at the same time, a distinct movement downwards towards the 

 south. The foldings of the rock as exposed to our view might 

 be compared to gigantic sheets of corrugated iron stacked up and 

 looked at endwise, but with this pecularity, that the stack was not 

 on level ground, but one end of each sheet was considerably 

 lower than the other. This endlong slope of the sheets is known 

 as " pitch," or among the Bendigo miners as " dip." The 

 pitch wherever we noticed it along the cutting was to the south. 

 The effect of pitch on the outcrop on a horizontal surface was 



