TRANSACTIONS OF SECTION C. 671 



set strikes N.N.E. and S.S.W., and forms an important escarpment, while the 

 upper set is folded over the central anticline of the district, and thrown again into 

 a syncline between Mucklewick Hill and Pell Rhadley HUl. The major part of 

 the paper was occupied by a description of the stratigraphy of the intrusive doler- 

 ites or diabases of the region, in which some new and striking features had been 

 discovered. 



These intrusive masses show, on the map, as large or small patches or as long 

 dikes striking in the same direction as the sedimentary rocks. Quarry and other 

 sections described clearly showed that these masses were not simple dikes or bosses 

 of the kind usually depicted in the published sections of the district, but had altered 

 sedimentary rocks resting conformably above and beloiv them, so that in appearance 

 they were lenticles bearing some resemblance to the Henry Mountain Laccolites 

 described by Gilbert. Instead, however, of owing their position to conditions of 

 simple hydrostatic equilibrium, these intrusions were shown to be intimately con- 

 nected with the folding which the district had suffered, and to stand to it in the 

 relation of effect rather than of cause. The Corndon and neighbouring Laccolites 

 have been forced, by hydraulic pressure, into spaces formed in the summit of the 

 main anticline, and were dammed down by the resisting mass of the rigid ash-beds 

 above them, so that the rock was intruded into soft shales between the hard rocks 

 of the Grit mine below, and the Stapeley (Upper Arenig) ash-beds above. In the 

 Linley Laccolite the intrusion was partly defined by the same ash-beds, but, where 

 the arch was broken, by the lower beds of the Silurian, while the Wilmington 

 Laccolite was entirely defined by the Silurian beds, the diabase resting on the 

 upturned edges of various members of the Ordovician sequence. These and the 

 other examples displayed clearly that the whole of the intrusive rocks of the 

 district might be reduced to one single system, being everywhere due to the effects 

 of lateral pressure operating upon alternating beds of rigid and soft rocks, between 

 and amongst which spaces, due principally to folding and secondarily to faulting, 

 were produced, and into these hydraulic pressure forced the molten rock. Intru- 

 sion can no longer be regarded as a mere sporadic and meaningless phenomenon, 

 but constitutes another volume of facts to speak for the extreme importance of 

 lateral pressure in giving to a rock region many of its structures and phenomena ; 

 and when this is once clearly understood, it will acquire a new meaning in unravel- 

 ling those portions of earth history of which the records are found in the present 

 structure of the rocks. 



In conclusion, the author thanked Professor Lapworth for suggesting many of 

 these ideas to him, and for help in understanding the precise meaning of the evi- 

 dence gathered. He also expressed his gi-atitude for a grant from the Royal Society 

 in aid of the petrographical work. 



2. Fourth Report on the Fossil Phyllopoda of the Falceozoic Eochs. — See 



Reports, p. 229. 



3. On the Discovery of Diprotodon Anstralis in Tropical Western Australia 

 {Kimberleij District). By Edwakd T. Hardman, F.B.G.S.I. 



To explain the extreme interest of this discovery it is necessary to recapitulate 

 briefly the history of the animal. 



Its remains, plentifully found in the south-eastern and eastern parts of Aus- 

 tralia, prove that it was a gigantic marsupial, probably belonging to the Macropo- 

 didas, or existing kangaroo family. Of immense size, its bulk was equal to that of 

 a rhinoceros, or even of an elephant ; the skull alone, as indicated by a specimen in 

 the Natural History Department of the British Museum, being 3 feet long. 



The head of the largest existing kangaroo is about 9 inches long, and his height, 

 sitting erect, about 6 feet 6 inches. Arguing from proportions, therefore, it might 

 be supposed that the diprotodon would in a similar posture be 18 feet high. How- 

 ever, though resembling in its dentition the living kangaroos, and, like them, herbi- 

 vorous in its habits, its anatomy shows important differences. The hind legs were 



