Posted by: Rob Viens | March 28, 2012

Of French Barons and Oil Seeps

On May 28th Darwin describes the crew hard at work on the primary mission of the Beagle – creating accurate maps of the coast of South America.  He notes:

“During these two days the labours of the expedition have commenced. — We have laid down the soundings on parts of the Abrolhos, which were left undone by Baron Roussin.” (Mar 27/28)

“Left undone” by the Baron or just done inadequately ? FitzRoy may hint at the  later:

“As far as we had time to examine, the chart of these islands, by the Baron Roussin, appeared to be satisfactory; but the soundings are so very irregular in the vicinity of the Abrolhos, that little dependence could be placed on the lead. More than once we had four or five fathoms under one side of the vessel, and from fifteen to twenty under the other. These sudden and startling changes, called by the French, ‘Sauts de sonde,’ are very unpleasant and perplexing.” (Narrative, Fitzroy)

Baron Albin-Reine Roussin was a French Naval officer that surveyed the coast of Brazil in 1819 (though apparently he left some gaps in this region). I’m sure that Fitzroy had copies of his maps on board. Roussin was no friend to Great Britton, in fact, before being involved in survey work he actively participated in several naval battles against the Royal Navy. A little more on the Baron at a later date…

Baron Albin-Reine Roussin (1831). Portrait by Charles Philippe Larivière:

Baron Albin-Reine Roussin

At the end of the day the Beagle approached the shallow waters around the Abrolhos Islands.  The water depth here was so variable and unpredictable that everyone was a little on edge as the Beagle approached the islands in the dark.

“The depth varied to an unusual extent: at one cast of the lead there would be 20 fathoms & in a few minutes only 5. — The scene being quite new to me was very interesting. — Everything in such a state of preparation; Sails all shortened & snug: anchor ready to let fall: no voice or noise to be heard, excepting the alternate cry of the leadsmen in the chains. — We anchored for the night” (Mar 27/28)

“We anchored near the islets, at dusk, on the 28th, after being in frequent anxiety, owing to sudden changes in the depth of water”(Narrative, Fitzroy)

While the crew was busy mapping, Darwin continued to observe interesting happenings on the ocean surface.

“To day at noon I observed the sea covered with an oily matter.— The thin globules displayed iridescent colours & were often time two inches in diameter.— A drop of water under a microscope showed on its surface minute globules of a transparent floating liquid, & which from its feel was of an oily nature… I am at a loss to conjecture what could have been the origin of such a quantity of oily matter; it is stated that whales often produce this effect.— At night this water showed luminous particles.” (Zoological Notebooks)

Then, later in October he went back and added the following comment in the margin:

“South of Corrientes: I observe some of the Pelagic Amphipods contain in the intestinal vessels a considerable quantity of coloured oil:— Entomostraca. The number of these Crustacea is often quite infinite” (Zoological Notebooks)

The term Entomostraca is no longer used – the organism that used to be lumped in this category were found to be quite unrelated types of Crustacea and were later reclassified.  Though one of the former members of the subclass were the copepods – which might be what Darwin describes here.  (Though I can find no reference to them producing an oily substance.)

I also doubt this was whale oil just floating randomly on the sea surface.  If I had to place bets, I’d guess that it was plain old “rock oil” (e.g., black gold, Texas tea, petroleum…).  Natural oil seeps are not uncommon – and wide continental shelves are potential oil reservoirs. And what do you know – according to offshore oil maps – this region does produce oil today.  I suspect on this day the Beagle was passing over the Espirto Santo Basin shown in the map below. Knowing this, I’d double my bet.

Oil-producing basins off the coast of Brazil (from RigZone via the Petroleum Insights blog)

Brazilian offshore oil producing basins

Of course, “rock oil” was still a long ways off from having any value, in so far as in the 1830’s society was still being powered by whale oil.  It would be another 50 years or so before people became interested in petroleum, and another 100+ yrs before we could drill for it on the continental shelf.

Tomorrow, the crew lands on the Abrolhos Islands – mayhem ensues… (RJV)


  1. Rob’s entry for today grounds us in the real mission of the Beagle: creating maps of the coast of South America. I have long had a love affair with maps. I can scrutinize them for time at length, even maps of cities, let alone states or countries. The map of Washington state is one of my favorite, following the changes from the Pacific Ocean to the Palouse and thinking about the climate, the vegetation, the rivers, the mountains. I like to think of the people that live in the various locales. For instance, why do people settle in Forks, WA vs. Seattle or Walla Walla and would they ever consider a change of venue?

    I think it is part of human nature to do map making and exploration and a cursory look at (“To the Ends of the Earth: 100 Maps that Changed the World”) indicates to me that many of us are fascinated by this endeavor or past time.

    • I agree – maps are truly works of art. I particularly like historic maps. I spent years pouring over historic charts of the coast of Alaska for my graduate work. Looking for changes to the glaciers over the years that were recorded on the maps. That and the field work are probably the most lasting (positive) memories from the project. Knowing the survey work that went into making these maps (especially before the 20th century) makes them all the more amazing.

  2. […] why he brought 22 of them). Finding that his measurements were off from Baron Roussin’s (see Of French Barons and Oil Seeps) raised some serious concerns. If his readings were already off after just a few month, then the […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s


%d bloggers like this: