It's obvious that Col. Fawcett and Mr. Wilkins are reporting on the same city from the same manuscript. However it should be noted that Col. Fawcett in telling of another “lost city” stated: It too was distinguished by the remains of a statue of a great black pedestal in the middle of a square. (Page 13). You can't help but wonder -- was this statue also pointing towards the north?
As Col. Fawcett continues his narration, his group is also following a river: fifty miles down (river) they came to a mighty waterfall, and in an adjoining cliff face were found distinct signs of mine workings. (Page11). Investigation proved the suspected mind shafts to be holes they had no means of exploring, but at the mouths lay scattered about a quality of rich silver ore. (Page12). This information leads one to the conclusion that it's obvious these 'holes', so deep that the witnesses “were never able to plumb their depths” was not the source of the rich silver oar found “scattered about.” No one would work a mine that you couldn't even walk into. But, I believe there is a simple, practical explanation. Historians tell us that even though the Spanish and others plundered many shiploads of gold, silver and other treasures from the peoples of the Americas, the thieves actually pilfered very little compared with what was hidden from the invaders. 
 
On pages 145-155 of Mysteries of Ancient South America Mr. Wilkins writes: Where do whispered native Quiche (direct descendents of the Inca Peruvians) traditions say these Lost Inca hoards lie? In sealed caves to which mystic hieroglyphs, whose key is possessed only by one descendent of the Inca at a time in each generation -- and in strange underground “Subterraneans”, thousands of years old which may have been made by a mysterious and highly civilized vanished race of South America in a day when ancient Peruvians themselves, were a mere wandering tribe of barbarians, if not savages, roaming the corilleras and the high passes.
Were Col. Faucett and his party on the trail of one of these “subterranean” of the vanished civilization when he disappeared into the unknown?

Trade Routes of the Ancients?

On page 167 Wilkins relates the story from about 1844, when a Catholic priest was called to the deathbed of an old Quiche Indian. The dying man told a story about “the closing of the amazing tunnel-labyrinths, by the high priest of the sun temple of old Cuzco, and the magicians, under the eye of the Imperial consort of the late Emperor Atahualpha.”
One of the approaches to the great tunnels lay, and still lies, near old Cuzco, but it is masked beyond discovery. This hidden approach leads directly into an immense “subterranean,” which runs from Cuzco to Lima, as the crow flies, a distance of 389 miles! Then turning southwards, the great tunnel extends into what until about 1868 was modern Bolivia, about 900 miles! [Emphasis by Mr. Wilkins].
He continues to tell of other connecting tunnels like the former Bolivian corridor (today located in Chili) runs southwards, passing through Yarapacca and Cobijo, which are in modern Chili. It must then turn eastwards, passing through or under the corillera and skirting the mysterious Atacama desert of Northern Chili. . . . The southern end of the tunnel is, thus, lost somewhere in this mysterious salt desert of Atacama (Pages 169-170).