The previous story, about the Volcanic eruption of the Rwenzori Mountains a few kilometers from our camp (“Fire on the Mountain“), actually occurred AFTER the story I’m about to tell. But I’m telling them out of sequence as a matter of character development. (The complexity of the real life situation significantly exceeds the complexity of this story line, as you may well imagine.)

I want to say a little about the research being done in the Semliki. After all, that is the reason we were there. There were quite a few different research projects, but I’ll mention only one now, because it was the central project of the Senga group, and I was mostly with the Senga group.

Also, the story of Senga 5a turns out to be an important story in the broader topic of African archaeology. You’ll see what I mean.

Senga, as I’ve told you, is one of many abandoned village names now used to designate paleontological or archaeological sites up and down the Semliki River. Although we dug many different sites at Senga, the main focus was one site in particular: Senga 5a.

Senga 5a is in the Western Rift valley. All of the securely dated and most ancient (pre 2.0 million year old) stone tools are found in East Africa, in the Eastern Rift Valley, with a few tantalizing prospects in South Africa. But the Western Rift was probably much wetter and had a lot of forest in these early days of proto-humanity, before about 2 million years ago. So, there is a hypothesis: Stone tool use by hominids was restricted to East (and maybe southern) Africa prior to 1.8 million years ago, when it may have then spread over a much larger area following shifts in forest vs. savanna cover. One way to falsify this hypothesis would be to look westward for a place with good preservation, which would be the Western Rift Valley, and find stone tools there. Unequivocal stone tools in 2 – 2.5 million year layers in the Western Rift would falsify the hypothesis, and this is how science progresses.

Plus, finding early stone tools would be just plain freakin’ cool in and of itself scientific method or not. So this work, while very high risk, was cool.

There were other sites in the area. Some of the most important early evidence of the manufacture of complex tools may be the Ishango Harpoons (some of which are quite old). There may be a very early calendar carved into a bone at Ishango. This is all very interesting and sometimes controversial, and I’ve included a number of references below for those interested.

I should also mention that the Western Rift is one of the places where the process of rifting (and thus, in part, of plate tectonics) was worked out early on, with much of this work having been done by Jean de Heinzelin. Jean did this work back in the 1950s and 1960s, and was invited to join the Ishango-Senga team in the year that the Congo Memoirs happened. Having de Heinzelin join your expedition is like working on a transplant team and having Christian Bernard show up to help. Or like working on some quantum physics thing and having Feynman show up to help. Or like … oh, never mind, you get the picture.

Only in our case, it was more like this: You are in the middle of your transplant surgery … say, installing a new liver in the patient … and the guy who invented transplants comes along, glances briefly in the body cavity and says, “Oh, you’ve got that upside down. Here, step aside. Let me do it.”

Or, you think you’ve just used a Feynman diagram to reconcile the problem of photon leakage from black holes of a certain size, and Feynman comes along and says, “Oh, that’s not a Feynman diagram. That’s a Sport’s Illustrated Swim Suit Calendar turned upside down! Here, let me show you how it’s done.”

Only in our case, it was like this: Two years of careful excavation of a “Late Miocene” archaeological site loaded with artifacts … hypothesis-killing 2.4 million year old unequivocally artifactual (hominid made) bits of quarts associated with piles of fossil bone of very extinct species type artifacts … is well under way. Then along comes Jean de Heinzelin, who is the guy who first figured out the geology of the place we were digging, and he has a brief look. And he says:

“Rubble!!!”

(Rubble?)

“This is Rubble!!!! You are digging in Holocene Rubble! (Oh, you’ve got to imagine this in a thick Belgian/Flemish accent booming from an older large man with a big scary beard and nothing to lose.) Can’t you see? The Bas Terrace (pronounced Bahs TehRass … ’cause it’s French) comes down here (making wide planar movements with the right arm) and cuts up the laterite layer here (chopping motions with the left hand) into little bits. It’s all mixed up, modern and ancient both all in the Rubble together. Little bits of Rubble. Holocene Rubble!!! You should have had me here two years ago. Boaz, you are such a nincompoop!”

Ooops.

Well, what happened after that is one of the most interesting episodes in African Archeology to ever occur, in my opinion. It happens that this very remote area was visited that year by a very rich team of experts. Everybody looked at Senga 5a very closely. The total number of scientists, including advanced PhD’s and very senior people who poked around on this site, took and/or analyzed samples, attended think-sessions, and so on and so fourth, was very large. Off hand I remember the following people being involved: A. Kay Behrensmeyer, Alison Brooks, Catherine Smith, David Helgren, Jack Harris, Jean de Heinzelin, Jeanne Sept, Jody Keating, John Gatesy, John Yellen, Kanimba Misango, Martha Tappen, Moi, Mzulendo Kibungia, Noel Boaz, Onus Kyara, Paul Morris, Peter Williamson, Randy Bellomo, Seleshi Semaw, and Tom Spang.

Now, as I recall, Bond and I were left to the very important but tedious and thus let-the-grad-students-do-it task of drawing the final profiles of the side of one of the holes we were digging, while Biker and Sileshi finished off some important topographic mapping tasks. My job in particular was to get on my stomach and poke and scrape at the 2,500,000 or perhaps 10,000 year old sediments and figure out what exact layers were visible, outline them with a sharp pointy object, and measure them in while Bond used my measurements to draw a picture of the profile … the visible wall left behind after excavation.

And when I did that I found a remarkable thing that had not been noticed before. I noticed that the brown sediment above the so-called rubble had an invisible line in it. I could feel it, and I could show it was there by scraping on it, but I could not see it. Below the line, the brown sediment was much harder and above it much softer. In other words, this line defined a layer of brown sediment beneath which was the “rubble” that some thought was over two million years old, and that others thought was less than 10,000 (probably closer to 6,000) years old.

Now, I believed that this archaeological site was older than 10,000 (and I still do) because the artifacts are technologically more like material greater than 250,000 years old. Or at least, some of the artifacts that we found ABOVE the rubble were clearly that old. Also, the fossils were clearly old. Rubble or not, these were 2 point something million year old extinct things. We knew this by comparison with other areas where we were not having these stratigraphic problems.

Well, this observation developed and to skip the boring parts, I managed to hold a sort court-like ceremony with most of the people mentioned above in attendance in which I demonstrated the reality of this layer of hard sediment, showing how the real distinction going on here was ABOVE, not below or within the Rubble. This meant that maybe it was actually ancient rubble, not Holocene rubble. Various scientists got down on their stomachs and poked at the profile. They scraped, prodded, they used their finger nails and tasted the dirt. The whole nine yards. At the end, all agreed that the layer was really there, but opinions differed as to its meaning.

Jean de Heinzelin was not convinced that the layer had any consequence. Big Red, who was in charge of this site and had in fact staked his career on this site, briefly stopped his pattern of despising and disrespecting me (noting personal, that’s just the kind of guy he was) and listened. Beherensmyer, the Queen of Taphonomy herself, stepped in to suggest that “The Greg Layer” (as she dubbed it) be taken seriously and tested further, and Paul Morris, a brilliant geologist working at that time way above his pay grade and I worked together with input from Biker, Bond and Joan to formulate a set of tests to determine where in this set of layers the Holocene stopped and the later Miocene/Pliocene began.

We spent the next couple of days taking special samples from the profile and elsewhere for use in the lab.

The main tests would involve using the volcano that I’ve mentioned earlier in these memoirs, the one that blew up and destroyed all live in the valley several thousand years ago. That volcano also left behind a strong chemical signature. We would be able to tell if the sediment of the Greg Layer was solidified before the volcano went off and subsequently uncontaminated by the absence of certain rare minerals. If the minerals were there, this would mean nothing (because these minerals could seep down into the sediment). But their absence would strongly support the case of the Greg Layer being very old. Or at least, older than de Henizelin’s Rubble Hypothesis required.

Turns out that our beautiful hypothesis was brutally murdered by the ugly facts pouring, months later in Paul’s lab at Harvard, out of various machines, showing the nasty volcanic minerals to be equally abundant within as above the Greg Layer. This did not mean that the pre-Greg Layer material was not old, but it did mean that we could not say it was old. (Other tests were also inconclusive). So today, we are left with the archaeological material of Senga 5a possibly representing an early (pre Middle Stone Age) assemblage, but not necessarily two million years old, and mixed with bones that the stone tools may or may not be linked to.

Oh well. Sorry, Big Red. I tried.

Tune in next week for the next installment of the Congo Memoirs, Kenyatsi, Place of Evil.

A. Brooks, D. Helgren, J. Cramer, A Franklin, W Hornyak, J. Keating, R. Klein, W. Rink, H Schwarcz, J. Smith, al. et (1995). Dating and context of three middle stone age sites with bone points in the Upper Semliki Valley, Zaire Science, 268 (5210), 548-553 DOI: 10.1126/science.7725099

J. Yellen, A. Brooks, E Cornelissen, M. Mehlman, K Stewart (1995). A middle stone age worked bone industry from Katanda, Upper Semliki Valley, Zaire Science, 268 (5210), 553-556 DOI: 10.1126/science.7725100

Alison S. Brooks, Catherine C. Smith (1987). Ishango revisited: new age determinations and cultural interpretations The African Archaeological Review, 5 (1), 65-78 DOI: 10.1007/BF01117083

Harris, J.W.K., Williamson, P.G., Morris, Paul J., Heinzelin, Jean de, Verniers, Jacques, Helgren, David, Bellomo, R.V., Laden, G., Spang, T., Stewart, K.M, Tappen, M.J. (1990). Arcaheology of the Lusso Beds Stratigraphy and Geological History of the Upper Semliki: A Preliminary Report

Verniers, Jacques, Heinzelin, Jean de (1990). Stratigraphy and Geological History of the Upper Semliki: A Preliminary Report Evolution of environments and Hominidae in the African Western Rift Valley

Marshack, A. (1972) Roots of Civilisation, The Cognitive Beginnings of Man’s First Art, Symbol and Notation, McGraw-Hill Book Company, New York