from the scientific standpoint.  The work of the archaeologists among the immeasurably ancient ruins of the low-land forests and the Andean plateaux is of this kind.  What Agassiz did for the fishes of the Amazon and what Hudson did for the birds of the Argentine are other instances of the work that can thus be done.  Burton’s writings on the interior of Brazil offer an excellent instance of the value of a sojourn or trip of this type, even without any especial scientific object.

Of course travellers of this kind need to remember that their experiences in themselves do not qualify them to speak as wilderness explorers.  Exactly as a good archaeologist may not be competent to speak of current social or political problems, so a man who has done capital work as a tourist observer in little-visited cities and along remote highways must beware of regarding himself as being thereby rendered fit for genuine wilderness work or competent to pass judgment on the men who do such work.  To cross the Andes on mule-back along the regular routes is a feat comparable to the feats of the energetic tourists who by thousands traverse the mule trails in out-of-the-way nooks of Switzerland.  An ordinary trip on the highway portions of the Amazon, Paraguay, or Orinoco in itself no more qualifies a man to speak of or to take part in exploring unknown South American rivers than a trip on the lower Saint Lawrence qualifies a man to regard himself as an expert in a canoe voyage across Labrador or the Barren Grounds west of Hudson Bay.

A hundred years ago, even seventy or eighty years ago, before the age of steamboats and railroads, it was more difficult than at present to define the limits between this class and the next; and, moreover, in defining these limits I emphatically disclaim any intention of thereby attempting to establish a single standard of value for books of travel.  Darwin’s “Voyage of the Beagle” is to me the best book of the kind ever written; it is one of those classics which decline to go into artificial categories, and which stand by themselves; and yet Darwin, with his usual modesty, spoke of it as in effect a yachting voyage.  Humboldt’s work had a profound effect on the thought of the civilized world; his trip was one of adventure and danger; and yet it can hardly be called exploration proper.  He visited places which had been settled and inhabited for centuries and traversed places which had been travelled by civilized men for years before he followed in their footsteps.  But these places were in Spanish colonies, and access to them had been forbidden by the mischievous and intolerant tyranny—­ ecclesiastical, political, and economic—­which then rendered Spain the most backward of European nations; and Humboldt was the first scientific man of intellectual independence who had permission to visit them.  To this day many of his scientific observations are of real value.  Bates came to the Amazon just before the era of Amazonian steamboats.  He never went off the native routes of ordinary travel.  But he was a devoted and able naturalist.  He lived an exceedingly isolated, primitive, and laborious life for eleven years.  Now, half a century after it was written, his “Naturalist on the Amazon” is as interesting and valuable as it ever was, and no book since written has in any way supplanted it.