302 ON THE TRANSMUTATION OF ROCKS, &c., 



locality no doubt can exist that the transmuting cause has been 

 the dyke of basalt below, and that the eruption was to some 

 degree violent. We may infer this from the fact, that between 

 the dyke and the sides of the cliff, there intervenes, besides the 

 aluminous matters, a bed of hard fractured sandstone pebbles. 

 Much of the clay that there exists takes the character of bole, and 

 that is often a clear indication of the presence of trap as at the 

 Giant's Causeway, where it exists among the basalt, and from 

 which the specimen was collected which is now before us. 



I have dwelt on the features of this Bondi locality, because it 

 illustrates more clearly than others all the principal characteristics 

 of such phenomena as are illustrated by it. 



At Botany Head, where the prismatisation has been intense, 

 the presence of igneous matter is not so clear. I have frequently 

 examined the cliffs to seaward very closely, but I have not found 

 any dyke. 



But, if we turn to Five Dock (which I have visited in company 

 of Professor Smith and Mr. Hunt) we have as it were an inter- 

 mediate example. There the sides of the quarry are about 

 twenty to twenty-five feet high in the deepest parts. The lower 

 members of the strata are all partially hardened, and the laminae 

 of deposit are apparent with layers of silicated alumina between 

 them ; yet soft as they comparatively are, they form well denned 

 polyhedral prisms by means of clean joints cutting through them, 

 of which the sides vary from nine to thirteen inches, and the dip 

 apparently fan-like, is on one side to N.W., on the other to S. 

 30 W. 



The beds on the north side themselves undulate in a sweep 

 inclining 5 E. and 8 W. ; the upper ten feet consisting of 

 thin beds of tile-stone, white clay and blue shale, with much 

 reddish clay, all of which have been greatly disturbed and 

 probably crushed during the partial upheaval and depression 

 which these rocks have undergone. 



One feature in this quarry is strongly marked. There is 

 much ferruginous matter in the normal rock ; but in the cal- 

 careous rock the whole of that red coloured stone is in the interior 

 of the prisms, as before mentioned. 



Now, though there can be no doubt that this quarry marks 



