AGASSIZ: THE GREAT HARRIER REEF OF AUSTRALIA. 109 



behind the conglomerate beds is fully six feet higher than the conglom- 

 erate. The bottom at our anchorage, only a short distance from the 

 face of the exposed flat, in ten fathoms of water, consisted of blue mud 

 and of broken shells. The faces of the elevated conglomerate exposed 

 to the action of the sea were pitted and honeycombed much as the 

 aBolian rocks of the Bahamas where exposed to the force of the sea. 



The next coral reefs we examined were those of the Palm Islands. 

 The corals off Great Palm Island rise from between four and six fath- 

 oms. They consist of masses of huge heads separated by coral sand 

 lanes, and extend to water of one and a half to two fathoms in depth 

 towards the shore. The amount of silt held in suspension in the water 

 was as great here as farther south along the inner Barrier Beef channel. 



Passing north from the Palm Islands (Plate XIX.), one cannot fail to 

 be struck at the marks of the extensive denudation and erosion apparent 

 on all sides. The domelike cliffs back of Townsville, the cliffs along the 

 railroad of the Boss Biver valley, the angular peaks, the sharp ridges, 

 the deeply cut valleys, the islands, islets, and rocks on the two sides of 

 Hinchinbrook Island passage, all indicate the effective work of atmos- 

 pheric agency (Plate XXX a .). 



The fine mud and silt which everywhere cover the bottom of the inner 

 channels of the Barrier Beef indicates only too clearly where the telluric 

 material has been swept to. In fact, this extends so generally over the 

 bottom, not only near the main land in close proximity to the lower 



by the piling action of the surf heaping up successive accumulations of calcareous 

 sand, which lias been subsequently compacted into rock. In the latter case, it 

 never could have reached a higher level than it now has (a few feet above high-water 

 mark), and its formation by this action must have required an immense period of 

 time, during the whole of which no depression can have taken place. Upon all these 

 flat spaces formed of this conglomerate, as well as upon all other flat land along the 

 eastern and northeastern coast of Australia, which is not more than ten feet above 

 high-water mark, there is found an abundance of pumice pebbles. ... By what- 

 ever cause they were cast upon the land, their present position proves that the 

 whole coast where they are found has been equally stationary, or equally affected 

 by movements of elevation or depression since they were so cast. . . . That the 

 advent of these pebbles is not a very recent event is proved by facts I observed on 

 the northeast coast. I have picked up pumice pebbles, for instance, on sand and 

 mud flats more than a mile from the sea. . . . Altogether, the evidence derived 

 from the existence of the coral conglomerates, and the presence of pumice pebbles, 

 to a height of eight or ten feet above the highest possible tides, proves to my mind 

 that for a very long period the whole eastern coast of Australia has either been 

 quite stationary, or has been affected by slight movements of elevation. It is 

 clear, I think, at all events, that no recent depression has taken place throughout 

 the district where either or both of these phenomena occur." 

 vol. xxviii. — no. 4. 2 



