"In my mind, only one thing possible accounts for their position.

You observe they appear to be about level with each other.
Well, once the Canyon floor ran along that line, and in the ages gone by it has lowered, washed away by the rains." This conception staggered us, but it was the only one conceivable.

No doubt we all thought at the same time of the little rainfall in that arid section of Arizona.
"How many years ?" queried Jones.
"Years! What are years ?" said Wallace.

"Thousands of years, ages have passed since the race who built these tombs lived." Some persuasion was necessary to drag our scientific friend from the spot, where obviously helpless to do anything else, he stood and gazed longingly at the isolated tombs.

The canyon widened as we proceeded; and hundreds of points that invited inspection, such as overhanging shelves of rock, dark fissures, caverns and ruins had to be passed by, for lack of time.
Still, a more interesting and important discovery was to come, and the pleasure and honor of it fell to me.