This explanation has always seemed to me unsatisfactory, because there are ample forests both in the temperate regions of the Andes and on the whole west coast down to Terra del Fuego; and it is inconsistent with what we know of the rapid variation and adaptation of species to new conditions.

What seems a more satisfactory explanation has been given by Mr.Edwin Clark, a civil engineer, who resided nearly two years in the country and paid much attention to its natural history.

He says: "The peculiar characteristics of these vast level plains which descend from the Andes to the great river basin in unbroken monotony, are the absence of rivers or water-storage, and the periodical occurrence of droughts, or 'siccos,' in the summer months.

These conditions determine the singular character both of its flora and fauna.
"The soil is naturally fertile and favourable for the growth of trees, and they grow luxuriantly wherever they are protected.

The eucalyptus is covering large tracts wherever it is enclosed, and willows, poplars, and the fig surround every estancia when fenced in.
"The open plains are covered with droves of horses and cattle, and overrun by numberless wild rodents, the original tenants of the pampas.
During the long periods of drought, which are so great a scourge to the country, these animals are starved by thousands, destroying, in their efforts to live, every vestige of vegetation.