154 The Volcanic Rocks of 



Volcanic conglomerate is another product of the Roman 

 hills. The circumstance under which we find it would lead 

 us to suppose that it was much more abundant formerly, and 

 that great masses have been washed off their old sites. A 

 hill of this conglomerate of fine ash and cinders exists near 

 Lake Bracciano, surmounted by a mediseval castle. The 

 famous citadel of Tusculum, not far from Albano, was 

 erected upon a rock of this substance, which itself stands on 

 a stream of lava. There is a variety of this rock, much 

 consolidated and studded with garnets, which is called by 

 the Italians Sx^erone, the lapis Tuscuktmis. It was in the 

 Neapolitan hiUs I saw a considerable amount of this 

 formation. 



In Victoria, the principal mass is on the Lawrence Islands, 

 off Portland. The danger attending the visit, from the 

 difficulty of landing, will not make it a popular resort for 

 tourists. I found the base rock of very consolidated cha- 

 racter. Part of it, consisting of ordinary tufa, and a dark 

 coloured, marly-looking volcanid substance, ran to points one 

 hundred feet and higher above the sea ; and upon which, on 

 different parts of the island, was the Cinder Conglomerate. 

 While some of these unrounded cinders were minute in size, 

 I noticed others a yard and more in diameter. A large piece 

 of wliite felspar had somehow or other got wedged in the 

 conglomerate. 



A few years, comparatively, will see the la^t of this great 

 curiosity of Victoria. The sea is constantly and successfully 

 warring against so feeble and friable a material. When I 

 was on the island, huge masses of the rock fell into the surging 

 ocean. Gulche-ways pierce the fortress for the rushing tides, 

 and resound with the scream of wild-fowl and the howling 

 of the storm. 



Having attempted an explanation of this formation some 

 ten years ago, I may be excused, perhaps, an extract from 

 that account, as I have not been able to repeat my visit : 



" In the earthquake which tilted the Portland limestone 

 westward of Cape Grant, it is not difficult to reahze the 

 action of a contiguous volcano. As no crater and no ashes 

 are known inland, within fifty miles, it is highly probable 

 that it was a submarine explosion. Some may imagine that 

 it may have been that which occasioned the basaltic field, 

 now recognized as Cape Grim, and the north-western islands 

 of Tasmania ; but from the prevailing westerly current, it 

 may be presumed that the volcano was situated somewhere 



