Letters from Mr. J. Graham Kerr. 269 



trict biologically. This is attributable in great part to its 

 intense dryness. Entirely of very recent formation, the 

 ground consists of a deep layer of light sandy soil, beneath 

 which appears in places a soft and slightly argillaceous sand- 

 stone. This pervious nature of the ground, combined with 

 the great heat and the intense dryness of the atmosphere, 

 favours evaporation to an enormous extent. As a consequence 

 the whole soil, except where by thick forest it is protected from 

 such evaporation, is strongly impregnated with salt. Flowing 

 into such a region, the streams of the Andes are, during their 

 passage across the Gran Chaco, to a great extent lost by ab- 

 sorption and evaporation, and in the case of most, where 

 there is any water left in them to reach the Paraguay, it is 

 intensely salt and bitter. During three fourths of the year 

 scarcely a drop of rain falls, so that the scantiness of the 

 flora is by no means to be wondered at. 



In its physical appearance the Gran Chaco in this portion 

 is an immense plain like the Pampas of Buenos Aires, or still 

 more the Llanos of the Orinoco, covered with a growth of 

 tall and coarse grass and thickly dotted with fan-palms, in 

 fact a gigantic palm-forest. Only occasionally is the extent 

 of palm-forest varied by a wide open meadow-like expanse 

 without a single tree or shrub, by a park-like stretch of green 

 turf with scattered trees and bushes, or by a comparatively 

 limited patch of dicotyledonous forest. This latter is not 

 forest of the majestic kind met with in Amazonia and other 

 parts of S. America, but is a dense aggregate of small and 

 slender trees some 15 to 20 feet in height, only here and 

 there amongst which shoots up an isolated tree of respectable 

 size. The undergrowth in such forest consists chiefly of 

 spiny Bromeliacese. Of aroids and ferns and other moisture- 

 loving plants there are few, for all is dry and parched. Such 

 patches of forest occur on ground slightly higher than the 

 surrounding '' palmar/' which latter occupies ground liable 

 to apparently annual inundation, as shown by the marks of 

 flood-level upon the palm-trunks. Borderiug the western 

 branch of the river more especially are extensive ranges of 

 what during much of the year forms marsh and swamp; but 



SEft. VI. VOL. III. U 



