398 Scientific Intelligence — Geology. 



had been employed for several years by Mr Lempriere, the deputy- 

 assistant Commissary-General, in accordance with my instructions, 

 and also to establish a permanent mark at the zero point, or gene- 

 ral mean level of the sea, as determined by the tidal observations 

 which Mr Lempriere had conducted with perseverance and exact- 

 ness for some time ; by which means any secular variation in the 

 relative level of the land and sea, which is known to occur on some 

 coasts, might at any future period be detected, and its amount de- 

 termined. The point chosen for this purpose was the perpendicular 

 cliff of the small islet off Point Puer, which, being near to the tide- 

 register, rendered the operation more simple and exact ; the go- 

 vernor, whom I had accompanied on an official visit to the settle- 

 ment, gave directions to afford Mr Lempriere every assistance of 

 labourers he required, to have the mark cut deeply in the rock in 

 the exact spot which his tidal observations indicated as the mean 

 level of the ocean. The tides in the Derwent were too irregular, 

 being influenced greatly by the prevalence of winds outside and the 

 freshes from the interior, so that we could not ascertain with the 

 required degree of exactness the point of mean level. It would 

 have been desirable to have fixed a similar mark on some part of 

 the opposite side of the island, but a prolonged series of preliminary 

 observations of the tides are necessary ; and as these had not been 

 obtained, and our limited stay, as well as the full employment for 

 all our observers, which the necessary experiments with the mag- 

 netometers provided, did not admit of our doing it, I can only hope 

 that some individual with like zeal for science with Mr Lempriere, 

 and with time at his disposal, may yet accomplish this desideratum. 

 I may here observe, that it is not essential that the mark be made 

 exactly at the mean level of the ocean, indeed it is more desirable 

 that it should be rather above the reach of the highest tide : it is, 

 however, important that it be made on some part of a solid cliff, not 

 liable to rapid disintegration, and the exact distance above the 

 mean level (which may also be marked more slightly) recorded on a 

 plate of copper, well protected from the weather, by placing a flat 

 stone with cement between, upon the plane surface or platform, 

 which should constitute the mark from which the level of the mean 

 tide should be measured. 



The most desirable position for such another mark would be near 

 the north-west extremity of the island, and in the vicinity of Capo 

 Grim, near which the Van Diemen's Land Company has a small 

 establishment. — Sir John C. Ross's Voyage to the Southern Seas, 

 vol. ii. p. 22. 



4. Active Volcanoes in the Arctic and Antarctic regions. — The 

 earth's crust, as we approach towards the pole in the southern 

 hemisphere, presents, in a remarkable degree, the most striking in- 

 dications of the vast subterranean fires pent up within it, and, as we 



