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Transactions . — Geology . 



vegetable debris, a foot or more in thickness, resting on the 

 sandy clay underlying the limestone, and out of which the 

 valley is excavated. 



It is in this talus that the bones are found, sometimes in 

 numbers near the top, sometimes deeply buried. An ex- 

 amination of the top of the cliff shows that at various dis- 

 tances from the edge along the whole line of cliffs are crevices 





Diagram of tjik Mode of Occurrknce of thf Bird -bones at 



Ngapara. 

 A. Limestone. B. Sands and clays. 



two or three feet in width — sometimes more — and these, I 

 believe, give the key to the question. It must be recollected 

 that before the advent of civilisation the country was covered 

 with dense masses of bushes and trees, and that birds were 

 numerous, so that open narrow fissures would in many cases 

 form eflicient traps for ground-birds. Let us suppose that 

 as soon as a crack opens (owing to the denudation of the 

 sandy clay underlying the stone) earth, leaves, and a few 

 birds drop in, together with sticks, leaves, and vegetable 

 dchru, until the fissure in course of time is full, when the 

 final slip happens, and the mass of limestone slips two or three 

 chains down the slope ; the contents of the fissure will gradu- 

 ally be distributed over the intervening space, a wide part of 

 the crack contributing more than a narrow part. Vegetation 



