Posted by: Rob Viens | November 20, 2013

Hamburger and Lime

On Monday the 18th, Darwin continued his leisurely trip by touring a local estate (Estancia) and learning a little bit about the daily routine of cattle ranching.  He described the experience as such:

“Rode with my host to his Estancia at the Arroyo de St Juan. — In the evening we took a circuit round the estate; it contained two square leagues & a half and was situated in what is called a rincon; that is one side is fronted by the Plata, & the two others are guarded by impassable brooks. There is an excellent port for little vessels, & an abundance of small wood, which is valuable as supplying fuel to Buenos Ayres. — I was curious to know the value of so complete an Estancia; — at present there are 3000 cattle & it would well support three or four times the number. — there are 800 mares, 150 broken horses, 600 sheep; plenty of water & limestone; a rough house, excellent corrals, & a peach orchard. — For all this he has been offered 2000£ only wants 500£ additional, and probably would sell it for less. The chief trouble with an Estancia is driving all the cattle twice a week to a central spot, in order to make them tame & to count them. This latter would be thought a difficult operation, when there are ten or fifteen thousand head together; it is managed on the principle that the cattle invariably divide themselves into little troops from forty to an hundred. — Each troop is recognised by a few peculiarly marked animals, & its number is known: thus one being lost out of ten thousand is perceived by its absence from one of the tropillas. During a stormy night the cattle all mingle together; but the next morning all the tropillas separate as before.” (Nov 18)

Route of Darwin’s trip into the interior of Uruguay (modified from Google Maps)

Map of Darwin's November 1833 Uruguay Trip

Notice the little yellow box above.  That is the site of the picture below.  Low and behold – there is Estancia Rio San Juan – likely to be the location Darwin was talking about today!

Map of Darwin's November 1833 Uruguay Trip

After a day of herding bovine herding on the ranch, Darwin rode through the “town of the cows” on his way up the river, writing:

“Passed the town of las Vacas; it is a straggling village, built on an arm of the Uruguay, & has a good deal of trade up the river. — Slept at a North Americans, who works a lime kiln on the Arroyo de las Vivoras.” (Nov 19)

OK – try finding a town named after cows in a part of the world where cows are around every corner.  I may have found Estancia Rio San Juan  But “Las Vacas” could be anywhere! (If anyone from the areas knows where Darwin might be talking about, please feel free to comment.)

On November 20th Darwin’s sights moved up the food chain from cows to jaguars.  And being the top predator that he was, we decided to go on a jaguar hunt.  Not to worry – no large cats were harmed in the writing of this diary entry, but Darwin did describe the experience:

“In the morning went out riding to Punta Gorda; on the road tried to find a Jaguar; saw very fresh tracks & the trees against which they are said to sharpen their claws: the bark was cut up & grooved by scratches a yard long: — we did not succeed in disturbing one. — The low, thick woods on the coast of the Uruguay afford an excellent harbour for such animals.” (Nov 20)

A lack of cats didn’t bother Darwin, because the natural world always held some new wonder for him.  In this case, it was the beauty of the Rio Uruguay that caught his eye:

“At Punta Gorda, the R Uruguay presented a noble body of water; its appearance is superior to that of the Parana from the clearness of the water & rapidity of the stream: on the opposite coast there are several branches, which enter from the Parana, when the sun shines, the two colours of the water may be seen quite distinct. — The house & lime-kiln were for this country unusually old, being built 108 years since. — I was told a curious circumstance respecting the Lime-kiln. — At the instant of the revolution it was full of fresh burnt lime; from the state of [the] country it was left 18 years untouched: on the surface young trees were growing, whilst in the middle the lime was quick. — When they dug down to the place where the half-burnt wood is left, in a few minutes it kindled & burst out into flames. — This caused uncommon superstitious fears amongst the workmen; but the owner tells me this is always the case in a lime-kiln opened after a few months interval.” (Nov 20)

Let me wrap up with a few words on “lime”. Lime, or more appropriately quicklime, is calcium oxide (CaO). (The term lime is more correctly used for various types of calcium oxides and carbonates.) Although quicklime has had other historical uses, its main use in recent centuries has been in the production of cement. Hence, it was a major ingredient in industrialization and urbanization, and the building of castles (see the figure below).

An old lime kiln burning in front of Dumbarton Castle, Scotland in 1800 (from Wikipedia Commons). It was not unusual to find these kilns on the water, which made transport of the fuel and finished product much easier.

Lime kiln at Dumbarton Castle

Quicklime is produced by extracting the mineral calcite from a type of sedimentary rock known as limestone (get it –a stone made of lime), and heating it to about 900-1000°C in a kiln, aka a lime kiln. Essentially, when heated limestone (calcium carbonate (CaCO3)) breaks down into quicklime (CaO) and carbon dioxide (CO2) gas.  The fires Darwin talks about above, would have been what provided the heat for turning the limestone into quicklime.

Finally, I can’t resist a word about limestone.

Last week I wrote about detrital sedimentary rocks – rocks made of fragments of other rocks.  The other major group of sedimentary rocks are those that form when dissolved elements recombine to form new chemical structures.  These are called “chemical sedimentary rocks”, and by far, the most common of these is limestone. Limestone can form in several different ways, but ultimately it is the result of the combination of dissolved calcium ions (Ca+2) and dissolved carbonate ions (CO3-2).  This combination can happen inorganically (resulting in the precipitation of calcite crystals from the water which accumulate to form the limestone) or it can be facilitated by living things that combine the ions internally and create shells and skeletons.  The hard parts of clams and corals form in this way, and when these organisms dies, their shells can accumulate at the bottom of the sea and create a different type of limestone.

A fossil-rich limestone from Germany (from Wikipedia Commons)

limestone

So where does the creation of limestone happen?  Well, to make a long story short, the conditions that tend to lead to the precipitation of calcite out of sea water occur where the water is warm and under low pressure. (The opposite conditions tend to cause “lime” to re-dissolve back into the water.) Based on these conditions and the fact that the bulk of the world’s limestones form in the oceans, it can be concluded that limestone is most likely to represent regions that were once shallow tropical oceans.  (There are some other places in which limestone can form. Most notably – cave limestones that form stalactites and stalagmites.)

In any case, my point here is that the presence of lime kilns in western Uruguay tells a geologist that this area contains limestone, which in turn means it was once under a shallow tropical ocean.  A far cry from the more temperate climate of the region today. (RJV)

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Responses

  1. I’ve nominated you for a ‘Blog of the Year’ Award- congratulations!
    You can see your nomination at http://mybotanicalgarden.wordpress.com/ and find ouit about the award at http://thethoughtpalette.co.uk/blog-awards-2-/blog-of-the-year-2013-award/
    Congratulations!

    • Thanks Tamara! As always I appreciate your support and am happy that you still enjoy the Beagle Project. Thanks for thinking of me for the award. And I am very happy to see that you were nominated as well.- Rob

      • I absolutely enjoy travelling with Beagle, I have some longer stops in between, but then try to catch up when I have more time , so thank you! Have a nice day! Tamara

  2. Great article! Do you have an idea of how old the limestones in that area are?

    • Thanks Alan! As far as I can tell from my generalized information, it appears to be Cretaceous. Sediments that accumulated on the craton after the breakup of Pangea. But I have never been on the ground here and my Spanish translation is not great, so I welcome comments from others who may know for sure.


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