(ieoUxjii of Li I (/(/(lie. 335 



inusaii- stiuclure of the theinuil iuetaiii<^i[)hisni is fiitiicly absent 

 It is therefore evident that consolidation here, as in thf liniestont 

 has been due chiefly to metasomatism, and possiljly also in somc^ 

 degree to dynamic metamorphism during the folding of tlu' \k'(\s. 

 This result is interesting inasmuch as thermal metamoipliism is tlu; 

 only process which Murray (7) and Stirling (8) suggested to account 

 for their alteration. The only instance of thermal nietamorphisnk 

 of the Silurian, that I have seen in the district, occurs along the 

 eastern shoulder of the Dandenong Kange, where the sedimentaries 

 have been converted into a hornfels. 



South of Cave Hill the quartzites increase their dimensions gradu- 

 ally, spreading westwards, and giving place as they do so to a fine- 

 grained sandstone. (See Fig. 6, Plate XXX.) 



The limestone Ixmlder in the railway cutting is flanked imme- 

 diately on the east by these easterly dipping sandstones. Assuming 

 that it is in sifii, this Ijoulder appears to form part of the thin end 

 of a lenticular limestone formation, related to the Cave Hill strata 

 as per Fig. 6. In this case, assuming the absence of faulting, the 

 western limit of the Cave Hill formation lies as far to the west of 

 the quarry as the railway line, and possibly beyond it. 



The colonies of marine organisms, which formed the limestones,, 

 perished through the accumulation of sands, initiated probably by 

 a movement of uplift. But the same sands which killed them have^ 

 preserved their remains. Defended behind this quartzite rampart, 

 and sheltered by a roof of basalt, the limestones have escaped 

 destruction. 



The prevalence of other quartzite and sandstone ridges to the 

 north-east, in Gruyere. where they rise abruptly above the flats of 

 the Yarra, together with the occasional presence of conglomerate, 

 probably indicates the inception and progress of those movements- 

 of elevation, which caused the last retreat of the Silurian sea. 



The disposition of the Gruyere ridges appears to be causally re- 

 lated to the strike and folding of the beds. (See Fig 5, Plate XXX. > 

 They occur in two pairs, and each pair may be arranged along a 

 straight line, parallel to the strike of the beds, and therefore to 

 each other. Both lines strike 16 degrees east of north. (This 

 easterly divergence is matched between Lilydale and Coldstream 

 by a strike of 47 degrees to 53 degrees east of north, thus indicating 

 a strong lateral easterly thrust in the Silurians north of Lilydale. 

 Just east of Evelyn the strike diverges 38 degrees east of north.) 

 The eastern pair both have a crescentic shape, with the crescent 

 opening northwards. Of the western pair the northern one is also 



