42 THE VICTORIAN NATURALIST. 



dipping to the west between 30° and 90° ; but in many places 

 cleavage has been observed dipping 25° to 85° E. Sometimes, 

 though rarely, it coincides with the bedding. Ten chains west 

 from the starting point beautiful cleavage is seen in fine-bedded 

 clay slate ; where the more strongly developed planes intersect 

 bedding of slightly different colours the junction has been drawn 

 into finely serrated lines. 



At 52^ chains below the junction of the Myrniong Creek 

 with the VVerribee a peculiar structure has been developed in 

 massive blue crystalline beds. Where seen in section, numbers 

 of fine, light-grey, irregular, ripply bands can be clearly traced, 

 dippmg 30° W. So closely do these bands resemble bedding of 

 different colours that one might be easily deceived as to their 

 nature. Closer inspection, however, shows that these bands cut 

 through both legs of an anticline. From the westerly dip and 

 their position they most probably represent cleavage planes which 

 have been lost owing to the great change the slate bands have 

 undergone. 



Along the axes of folds a close-set radiating jointing has been 

 developed. Very frequently thin sheets or films of quartz have 

 formed in the wider joints. This fine jointing is best observed in 

 the finer argillaceous beds. Spurs and veins of quartz, several 

 inches in thickness, penetrate the fractures in the quartzites and 

 sandstones on the crest and in the trough of anticline and 

 syncline. Where alternating bands of clay, slate, and sandstone 

 occur, cleavage has been developed in the former beds, and to 

 such a marked degree that had the sandstones been absent it 

 would be impossible to ascertain the true dip. 



Over the whole Silurian area the strike is fairly constant, vary- 

 ing from N. 2° E. to N. 15° E., generally N. 10° E. 



Numerous quartz-felsite and other dykes cut the Silurians, 

 almost always through or near to the axis of an anticline — that is, 

 in a more or less north and south direction. Several examples 

 can be seen in the cuttings on the Melbourne-Ballarat line, east 

 from Ingliston, and also to the north and south of the pile bridge 

 on the same line, and in the Werribee Gorge. At right angles to 

 the above there is a second series, which cut both the Silurians 

 and older dykes, often passing into the overlying glacial beds. 

 An example of this can be seen a few yards below the junction of 

 the Myrniong Creek with the Werribee, where a branching 

 almost vertical dyke has weathered out, leaving narrow openings. 



Darwin when at Albany observed a series of parallel dykes 

 running east and west, and not far away a second series of eight 

 ranging at right angles to the former ones. 



In passing I might mention that all the quartz-felsite dykes are 

 of much greater age than the glacial deposits of Bacchus Marsh. 

 There is not the least evidence to support the theory that the 



