chap. vii. Great Valleys. 151 



depth between 60 and 70 feet, has been observed l to be 

 broadly rippled. One may, therefore, be allowed to 

 suspect, from the appearances just mentioned in the 

 New Eed sandstone, that at greater depths, the bed of 

 the ocean is heaped up during gales into great ripple- 

 like furrows and depressions, which are afterwards cut 

 off by the currents during more tranquil weather, and 

 again furrowed during gales. 



Valleys in the sandstone platforms. — The grand 

 valleys, by which the Blue Mountains and the other 

 sandstone platforms of this part of Australia are pene- 

 trated, and which long offered an insuperable obstacle 

 to the attempts of the most enterprising colonist to 

 reach the interior country, form the most striking 

 feature in the geology of New South Wales. They are 

 of grand dimensions, and are bordered by continuous 

 lines of lofty cliffs. It is not easy to conceive a more 

 magnificent spectacle, than is presented to a person 

 walking on the summit-plains, when without any notice 

 he arrives at the brink of one of these cliffs, which are 

 so perpendicular, that he can strike with a stone (as I 

 have tried) the trees growing, at the depth of between 

 1,000 and 1,500 feet below him ; on both hands he sees 

 headland beyond headland of the receding line of cliff, 

 and on the opposite side of the valley, often at the 

 distance of several miles, he beholds another line rising 

 up to the same height with that on which he stands, 

 and formed of the same horizontal strata of pale sand- 

 stone. The bottoms of these valleys are moderately level, 

 and the fall of the rivers flowing in them, according to 

 Sir T. Mitchell, is gentle. The main valleys often send 

 into the platform great bay-like arms, which expand at 

 their upper ends ; and on the other hand, the platform 



1 M, Siau on the ' Action of Waves : ' « Edin. New Phil. Journ. 

 vol. xxxi. p. 245. 



