AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 125 



which it originally extended. . . . After the Rolling Downs formation 

 had been laid down in the comparatively narrow sea which connected 

 the Gulf of Carpentaria with the Great Australian Bight, and converted 

 the Australian area into two islands, a considerable upheaval took place. 

 The denudation of the Rolling Downs formation then followed, and must 

 have gone on for some time. Unequal movements of depression then 

 brought about lacustrine conditions on portions of the now uplifted 

 bottom of the old deep-sea strait, and in other portions permitted the 

 admission of the water of the ocean. Finally a general upheaval placed 

 the deposits of the period just concluded in nearly the position in which 

 we now find them." 



Jack considers that " The absence ... of tertiary marine strata may 

 be due to the fact that the elevation which took place after the deposi- 

 tion of the upper cretaceous rocks (desert sandstone) placed the whole 

 of Queensland above the reach of the ocean during tertiary times." 

 (Geol. and Pal. of Queensland, p. 574.) 



These extracts from the past history of Queensland are important, as 

 they clearly indicate the great length of time during which the eastern 

 extension of the Queensland coast has been exposed to the effects of 

 denudation and to the inroads of the sea, — inroads the extent of which 

 is cleai-ly indicated by the islands and archipelagos skirting the north- 

 east edge of Australia, and the extent of the denudation is plainly vis- 

 ible in the shape of the hills and valleys flanking the present coast line. 



Jack (Geol. and Pal. of Queensland, p. 613) gives the following proof 

 of a moderate depression of the Queensland coast : "In the neighbor- 

 hood of Townsville a well reaching to one hundred feet in depth shows 

 the presence of clays and gi'avel belonging to river beds which fringe the 

 coast from Cape Palmerston to the mouth of Herbert River. No river 

 could possibly have excavated a channel to this depth while the land 

 stood at its present level ; it must have been depressed to or beyond the 

 position at which it now stands with refei*ence to the ocean." 



Fragments of this lost land, he considers, " remain in Fitzroy, Hinchin- 

 brook, the Palm and Percy Islands, . . . while a submerged range still 

 farther to the east may be represented by the Barrier Reef." 



It seems to me that, in addition to the above mentioned submergence 

 of one hundred feet, we must take into account the extensive denudation 

 and erosion which Jack himself has so well described in the paragraphs I 

 have quoted from him. A denudation and erosion which, acting through- 

 out the tertiary period, a period of great fall of water, are of themselves 

 quite sufficient to explain the former connection of the islands off the 

 vol. xxviii. — >o. 4. 3 



