37o NATURAL SCIENCE. Nov., 1893. 



The occurrence in chalk Downs, and in hills of similar porous 

 strata, of deep valleys in which no streams now exist even after the 

 heaviest rain, and the existence of enormous sheets of irregularly 

 stratified or rubbly gravels in the lowlands adjoining, instead, there- 

 fore, of constituting the strongest evidence in favour of the existence 

 of a Pluvial Period, seem more probably, like the fossils, to point to 

 the occurrence of cold desert periods, when the rainfall, though small, 

 could act much more energetically as a denuding agent. Under such 

 conditions it is possible to understand the correlation of a fauna 

 poor in truly aquatic species with deposits indicating violent floods. 

 The absence of subterranean drainage would not only cause violent 

 floods, even with a small rainfall, but would lead to the disappearance 

 of the springs and consequently of all perennial streams except such 

 as drained a large area. This, again, would tend to emphasise the 

 desert character of the fauna. 



REFERENCES. 



1. Nehring, Alfred. — Ueber Tundren und Steppen. Berlin, 1S90. 



2. Reid, Clement. — Dust and Soils. Geol. Mag., Dec. 3, vol. i., p. 165, 1884. 



3. . — On the Origin of Coombe Rock and of Dry Chalk Valleys. 



Quart. Jouvn. Geol. Soc., vol. xliii., p. 364, 1887. 



4. . — On the Pleistocene Deposits of the Sussex Coast. Ibid., 



vol. xlviii., p. 344, 1892. 



Richthofen, F. von. — On the Mode of Origin of the Loess. Geol. Mag. 

 Dec. 2, vol. ix., p. 293, 1882. 



Smith, W. G. — Primaeval Man : A Palaeolithic Floor near Dunstable, Nat. 

 Sci., vol. L, p. 665, 1892. 



Woodward, A. S. — Note on the Occurrence of the Saiga Antelope in the 

 Pleistocene Deposits of the Thames Valley. Proc. Zool. Soc, 1890 (1891), 

 p. 613. 



Clement Reid. 



