HOW FAR VEGETATION IS A PROOF OF RAIN FALL. 
173 
drawn from such results, and applied to the interior of a continent, under latitude 32°, must he 
erroneous, unless the considerations to which I have alluded he attended to.* 
Nothing is more common than the loose verbiage in the mouths of many, that, the geological 
circumstances being favorable, artesian wells are possible to be produced. 
This may he true in north Europe and along our Atlantic coast, where the rains are constant, 
and to a high figure ; hut it is not true in the Gadsden Purchase, because the climatal relations 
approach that of the tropical zone. 
An objection may he raised to the arguments advanced and the conclusion drawn, based upon 
imperfect observations of the climate. It may he said that the registers of Fort Yuma, and 
those on the Rio Grande, afford no index of rain fall of the country between these points, and 
that, as the country inland is more elevated, it is hub reasonable to suppose that a large supply 
of rain does exist. The reply to this objection is, that no matter how ignorant we may he of 
the actual rain fall, as estimated by a rain gauge, yet that there are always evidences suffi¬ 
cient in the district furnished at once, and visible at a single inspection, which can lead to an 
approximation of the actual fact. These evidences are, the appearance of the water-courses, and 
the character—the species—of the vegetation natural to the district. 
If the water-courses be short, if the bed be rugged, filled with large stones, washed out from 
above and impacted in gravel, and if it suddenly terminate by opening upon plain land, and 
does not empty into another channel or river bed, then it is the course of a short and tumul¬ 
tuous body of water, collected together suddenly, and rushing along in a mass, and not in a 
continual stream—it is a torrent and not a river. It does not signify how deep the sides of the 
water-courses are—these do not indicate long continued and low action ; a small creek, sud¬ 
denly emptying into the Hudson river below Newburg, has (in 1852) in one night excavated 
a hank 60 feet deep ; it is but the evidence of force or power of water, hut not of its actual 
quantity, or of its continuance of action. 
Especially is this true where it does not empty into a larger stream bed ; it shows that the 
total quantity has been too small to prolong it into a stream. Numberless are the arroyos or 
creek beds of this character, which give out, or lead to nowhere. 
Again, with regard to the evidence derived from vegetation. This is more certain than the 
other. Let us consider a district which has no subterranean supply of water, and wholly 
dependent upon the rains. Suppose such a district to be wholly destitute of vegetation, the 
observer would infer either of two things : 1st, that no rain at all fell, or that it did not fall at 
the time favorable to vegetation. The first supposition is improbable, as we know there are 
few places on the globe where some rain (slight though it he) does not fall; and it is not true 
of any locality on the route, for in some of the most barren localities the arroyo beds were 
found; and in others, as the playas, the surface was ripple-marked by superjacent water. 
With regard to the second supposition, that it did not fall at the favorable time to benefit vege¬ 
tation, it may be worth while to inquire into its meaning : Is there any time peculiarly favor¬ 
able to vegetation ? are plants so obstinate, and such formalists, as to grow in exact months in 
spring time when it does not rain, and refuse to grow in summer when it does? 
Our knowledge of vegetation shows that plants will grow when the supply of moisture in the 
ground is sufficient to carry the food it requires in a liquid state to its roots ; it cannot grow 
until after some rains, nor mature itself until after more ; and that, let it he supplied with 
* The artesian, borings, as they are called in California, are not cases in point; they are, in fact, not artesian wells, but 
simply deep clay borings. 
