198 
ARE SOILS ENRICHED, IMPOVERISHED, [Part III. 
or branch dry valleys are there falling into the 
main longitudinal dry valley whose lower end 
joins the upper end of the river valley ? And 
how many lateral or branch dry valleys fall into 
the main river valley ? And what formed these 
countless myriads of dry valleys ? 
These valleys exist even in volcanic countries, 
where the sea could not have formed them while 
the land was emerging; and the gradients of 
the river valleys and dry valleys, and the whole 
form of the ridges and furrows, of the entire sur¬ 
face-drainage of a volcanic region (say, of Ma¬ 
deira) are so precisely the same as those of any 
other mountainous district, that no eye can 
glance over the two and doubt for an instant 
that the same cause caused the form of the 
drainage of both. 
In fact, rain, which we consider only as a pro¬ 
ductive power, is the destroyer, the dissolver, of 
continents. Subterranean igneous action, which 
we consider only as a destructive power, is the 
producer, the replacer, of continents. And 
the cause which caused the valleys is in as full 
operation at this moment as ever it was. Indeed, 
valleys only exist in the dissolution of hills; 
that is, in the gradual and eternal wash by rain 
of the existent earth into the sea. 
