Posted by: Rob Viens | July 6, 2012

Darwin and the Finger of God

At last Darwin was “on the road”, but alas, on the evening of July 6th –  two full days out of port – they had not gotten very far:

“Scarcely any wind. The Sugar Loaf is still in view & points out the entrance into Rio.” (July 6)

FitzRoy adds a positive spin on the situation:

“A few leagues southward of the port is a good situation for enjoying a general view of the picturesque mountains in its vicinity. When near the shore one only sees those of an inferior order; and it is not until an offing is gained that the bold and varied outlines of the distant Organ Mountains, the sharp peak of the Corcovado, and the singular heights over Tijuca, can be seen at once. Whimsical allusion has been made to the first Lord Hood in the name by which one of these heights is called by English sailors; and in their general outline is a fancied resemblance to a huge giant lying on his back.” (FitzRoy’s Narratives)

1880 print of the Organ Mountains (artist unknown):

Organ Mountains, Brazil

I’ve discussed the other peaks before, so I’ll share a couple words about the Organ Mountains on this quiet Friday night…

The Organ Mountains (Serra dos Órgãos), located just inland from Rio, were named because of their resemblance to the pipes of a cathedral organ. At least ten of these “pipes” rise to over 2000 meters (6,600 feet).  Their elevation helps lend biodiversity to the Atlantic Coastal Forest (see The Stupendous Pleasures of the Atlantic Coastal Rainforest), and partially in recognition of this the region around the mountains was protected as a National Park in 1939 (Brazil’s third national park),

1910 watercolor “At The Back of The Organ Mountains” by Archibald Stevenson Forrest:

Organ Mountains, Brazil

From what I can tell from online reports (my Portuguese is not good – ok nonexistent is a better word), the Organ Mountains are made primarily of granitic intrusions (much like Corcovado and Sugerloaf mountains).  A 2003 paper dated all the granite intrusions in the 560 to 580 million year range (late Precambrian).  They would have formed as part of a very old subduction zone – long before the formation of Pangea.  As noted in earlier posts, the peaks themselves are most probably the result of differential erosion – the relatively softer surrounding rocks weathering away first and leaving the harder granitic intrusions behind as peaks.

Organ Mountains – the distinctive “pointy” peak is called “God’s Finger” – Dedo de Deus (from Wikipedia Commons):

Organ Mountains, Brazil

Interestingly, the Swiss geologist Louis Agassiz also traveled in Brazil in the late 1800’s and took an excursion to the Organ Mountains.  His book, A Journey in Brazil, can be found on Google Books. Of course, being the father of glacial geology, he sees evidence for glaciers everywhere…(RJV)

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