34 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov, 20, 



five miles distant from Hobart Town, which had entirely altered the 

 physical features of a considerable portion of that district, besides 

 causing loss of life and wide-spread desolation. 



Upon the cessation of the storm, I at once started for the scene 

 of the catastrophe ; and, upon arriving at O'Brien's Bridge, I found 

 that rumour had not in this instance travelled on the wings of ex- 

 aggeration. From this point, distant five miles from Mount Wel- 

 lington, it could be seen that a large portion of the northern face of 

 that mountain had given way, and, descending to a depth of nearly 

 2000 feet into the bed of the rivulet which takes its rise at that 

 point, had carried destruction and desolation on either hand. This 

 mountain-torrent, after pursuing a very tortuous course, and having 

 a mean descent of 9° for about six miles from its source, empties 

 itself into the river Derwent, about one mile from the township of 

 Glenorchy. 



The scene which presented itself at this locality was one that 

 could never be forgotten. Huge trees, some of them more than 

 200 feet in height when standing, were piled up in vast heaps, pre- 

 senting an entangled mass of timber, boulders, casks, fences, agri- 

 cultural implements, and various other objects. Such had been the 

 force of the torrent that not a vestige of bark, branches, or roots 

 could be seen for the most part on these transported trees, while 

 even the blue gum {Eucalyptus globulus), which is among the hardest 

 and toughest of Tasmanian woods, not only had its massive pro- 

 tuberances ground down smooth with the trunk, but reduced to 

 fibre where the trunk had been snapped short off. 



Finding it completely impracticable to approach the landslip on 

 this occasion, owing to the condition of the country, I was compelled 

 to return ; but I renewed the attempt a few days afterwards. 

 Starting from O'Brien's Bridge, I took up the bed of the rivulet. 

 This I found to be occupied by carboniferous limestone, a formation 

 which is well developed in this part of the island. This limestone, 

 which, as a rule, teems with Brachiopodous remains (the most abun- 

 dant of which are Spirifera producta and Terebratulce) and an equal 

 abundance of Bryozoa, has been exposed by the erosion of the torrent 

 for more than two miles. In those places where the debris deposited 

 by the flood have left natural sections of this formation fully exposed, 

 I find the blue, crystalline, shelly limestone alternating with beds of 

 mudstone and thin inter stratifying shales. I mention this fact for 

 the reason that hitherto Tasmanian geologists have regarded the 

 mudstone deposits as upper members of the Carboniferous limestone 

 series. This mudstone, I may observe, contains, as far as known, 

 the same species and genera of fossil Testacea and corals as the true 

 limestone ; but it differs from the latter in the important particular 

 of yielding only the casts of those organisms — being, in short, entirely 

 devoid of carbonate of lime. 



At the distance of one mile, or thereabouts, from O'Brien's Bridge, 

 I found still more striking evidence of the power of the torrent than 

 that already referred to. This consisted in both banks of the rivulet 

 being lined for a considerable distance with small angular fragments 



