A Response to Giza: The Truth
by David P. Billington, Jr.
Copyright 2000.
In their recent book, Giza: The Truth (Virgin Publishing, London 1999), Ian Lawton and Chris Ogilvie-Herald challenge a number of alternative theories about the ancient Egyptian monuments at Giza that have attracted recent attention. An important part of the book (chapter seven) discusses the efforts of John Anthony West and Robert Schoch to redate the Great Sphinx. In my comments below, I would like to respond to what Lawton and Ogilvie say about West and Schoch.
I should note that my comments below refer only to chapter seven. I have not read the rest of their book (I am waiting until it comes out in revised paperback form).
My approach to the Sphinx age question resembles and differs from the approach taken by Lawton and Ogilvie. Like them, I have approached the controversy with no formal training in Egyptology or related scientific disciplines, and I have had to educate myself on the issues in dispute. Like theirs, my own views have also evolved. I differ from Lawton and Ogilvie in giving greater weight to the evidence in favor of an earlier date, and consequently have greater respect for the work done by West and Schoch. But I also take seriously the views of critics.
I have maintained a website on the Sphinx controversy since the spring of 1996. (Ian has told me that he and Chris did not visit my site in preparation for their book.)
Robert Schoch has given me permission to repost his own comments on my website. I have placed a link to these at the end of my own comments below as well as here.
Lawton and Ogilvie have recently posted comments that take into account the arguments of a geological engineer, Colin Reader, who examined the Sphinx and its enclosure in the mid-1990s.
I have divided my comments below into a discussion of detailed points followed by discussion of a few general ones.
Detailed Comments
The seventh chapter of Giza: The Truth cannot be discussed analytically in the exact order of the arguments and evidence it presents. The content needs to be regrouped under five headings: ancient rainfall, sub-sand weathering, surface weathering, sub-surface weathering, and archaeological context, and considered in that order.
Schoch's 1992 KMT article provides an overview of the original West-Schoch hypothesis. In the article, Schoch argues that the erosional features on the Sphinx and its enclosure walls show evidence of heavy rainfall. In his view, the necessary rainfall to cause this erosion has not fallen in the time since the traditional date scholars give to the carving of the Sphinx c. 2500 BCE. The surface erosion persuaded West and Schoch that the Sphinx dated to late prehistory, when rainfall was more abundant in Egypt. Evidence of sub-surface weathering more concretely indicated a late prehistoric date (c. 7000-5000 BCE, possibly earlier). The initial arguments of West and Schoch in the early 1990s have undergone further development since then, but the idea of a prehistoric Sphinx remains their central thesis.
Ancient rainfall. Lawton and Ogilvie begin their critique on pages 311-315 by questioning whether the rain that fell in Egypt over the last 4500 years was insufficient to produce the erosional features attributed by Schoch to prehistoric rainfall. They cite historical accounts of heavy if sporadic rainfall in the last 4500 years to argue that the climate was not totally arid. They also note that rainfall diversion work on the roofs of ancient Egyptian temples suggests that rainfall in ancient times may have been significant.
The historical accounts that Lawton and Ogilvie cite are anecdotal in nature and do not change the fact that we really don't know how much rain fell in the last 45 centuries, except that in aggregate it was much less than in late prehistory. It does not necessarily follow that rainfall since 2500 BCE was insufficient to cause erosion, because we do not know the rate at which the rock in dispute eroded. But neither does evidence of sporadic heavy rainfall establish that such rainfall was enough to cause the disputed erosion.
Rainwater catchment channels and diversion spouts on temple roofs show that rain fell in dynastic times. But these features do not necessarily indicate more than the very low average annual precipitation of today. The temples of Egypt had elaborate and ritually important paintings on their walls. The paint was water-resistant but rainwater falling on temple roofs picked up dust and sand, forming a slurry that could deface and strip off the paint if it was not diverted. Channels and spouts were necessary even if rain fell only rarely. Consequently, they cannot be regarded as evidence of regular and significant rainfall.
Sub-sand weathering. The Sphinx lies in an excavated enclosure that has been filled with desert sand for about two-thirds of its known existence. This sand cover has buried the monument up to its neck and protected the Sphinx from certain kinds of weathering in the open (discussed under surface weathering below). James Harrell, a geologist critical of Schoch, has proposed that wetting of the sandcover could have eroded the Sphinx during the centuries it was covered.
On pages 313 and 319-320 of their chapter, Lawton and Ogilvie present Harrell's theory. Harrell argues that capillary action (suction) from the water table and from nearby Nile flooding, and occasional rainfall, wetted the sand regularly. This wetness in Harrell's view caused chemical activity on the Sphinx body that caused it to erode. Chemical weathering is known to take place when the Sphinx is exposed to the air. Capillary action pulls morning dew into pores in the rock surface, where it mobilizes salts that dry and expand later in the day. In smaller pores, the expansion stresses the rock and causes it to flake off. Chemical weathering has accelerated under the air pollution of recent decades. Harrell argues that chemical degradation (mainly salt exfoliation) could occur under wet sand.
The more friable strata of the lower body of the Sphinx should have had more erosion than the harder upper strata of the body as a result. Lawton and Ogilvie acknowledge that the upper body in fact shows more erosion, not less, a finding that lends support to rainfall as the cause. Schoch pointed this out in a reply to Harrell that Lawton and Ogilvie neglect to cite. But on page 320 Lawton and Ogilvie conclude: "However, if we accept that the 'arid' climate in Egypt has continued to produce sporadic but intense rainfall, then we can surely argue that this mechanism would have been at work from the top down as well."
The mechanism in the above sentence cannot be Harrell's. If the upper body was exposed to direct rainfall, then the resulting action would have been physical weathering, a mechanism quite different from chemical weathering of the wet-sand kind argued by Harrell. If the upper body was not exposed directly to rain (and the affected sections seem to have been covered), then only chemical weathering of the wet-sand kind would have taken place during periods of sand cover. But whether such weathering actually caused the erosion on the Sphinx may be doubted if the body of the monument failed to weather as the wet-sand theory predicts.
In their exchange over wet-sand, neither Harrell nor Schoch note that the main body of the Sphinx may have been covered with facing stone blocks for long periods. Chemical weathering of the main body could not have penetrated these. The greater weathering of the upper body might be explained if the lower body facing stonework was intact while the upper facing had either broken down or was never completed. However, the Egyptologist Mark Lehner found in a 1979 survey of the Sphinx that the earliest facing stone conformed to an already weathered profile of the main body (see my general comments farther below).
Surface weathering. On pages 315-316, 318-319, and 320-321, Lawton and Ogilvie turn to the question of whether other kinds of weathering besides rainfall could have produced the surface erosion on the Sphinx and its walls during periods when the enclosure was free of sand. They cite a geochemist, K. Lal Gauri. In a 1995 article, Gauri notes that in chemical weathering caused by morning condensation, the stratification of rock determines the weathering profile. Different horizontal gradients (sub-strata defined primarily by pore size differences) in the rock will produce horizontal rolls of the kind we see on the Sphinx (small pore rock will weather back more deeply). Gauri sees this kind of recession as evidence that chemical effects were the major cause of weathering to the Sphinx and its enclosure walls.
This does not explain the vertical fissuring and rounding on the Sphinx and especially its walls that constitutes the main evidence for heavy rainfall. These vertical features cross-cut the gradients that produce horizontal erosion and cannot therefore be explained by such gradients.
Natural vertical faulting occurred in the rock of the Giza area millions of years ago. Gauri acknowledges that as these faults became exposed, they could have been widened and rounded by rainfall. But he attributes the fissuring of the Sphinx and its walls primarily to subsurface water movements (the rising and falling of water tables) underground over millions of years. Joints widened in this way do exist on the Sphinx. But David Coxill, a geologist who has examined the Sphinx and its walls, has pointed out that water movements of this kind do not produce fissures that are wider at the top than at the bottom. Such fissures also exist and are especially clear on the western end of the enclosure walls.
Lawton and Ogilvie point out that rounded rock continues to weather in a rounded way under present-day conditions without much rain. Therefore, they argue, it could have eroded that way under similar (ie. relatively dry) conditions in the past. It is not clear, however, whether this erosion is evenly spread across pre-weathered surfaces or is preferentially shaping these surfaces to be round and wider at the top. To explain Schoch's observations, any chemical explanation must also act on the same rock in the same way, and there is evidence that the same rock in the enclosure has not weathered identically (see discussion of Colin Reader below).
Gauri really establishes a complementary form of weathering, not a contrary explanation of the same weathering features that concern Schoch. Schoch addressed condensation weathering as early as his 1992 KMT article and he noted that it is the least destructive of the three principal mechanisms that are known to have weathered the Sphinx: rain, wind-blown sand, and condensation.
West and Schoch devoted considerable effort in their early work to distinguishing rain weathering from weathering by wind-blown sand. Lawton and Ogilvie argue that the two kinds of erosion commingle on exposed rock and they argue, somewhat unclearly, that the two kinds are difficult to distinguish but that they can be distinguished enough to know that one can erase evidence of the other (pages 316-317).
The erosional features that suggest rainfall are the quite obvious fissuring and rounding of hard upper surface rock on the enclosure walls. Wind erosion can produce rounding, as it does on the corners of core blocks in some Giza temples, but wind-blown sand doesn't form gulleys in rock. The differences between wind and rain erosion proved difficult for West and Schoch to debate, however, in part because Schoch and West relied on examples of wind erosion that lay outside the Sphinx enclosure. Critics charged that these examples belonged to different (and therefore incomparable) layers of rock.
The entire debate was also troubled by the fact that we don't know the rate of weathering in surface rock, a basic uncertainty that Lawton and Ogilvie mention only as an afterthought on pages 321-322. But an important question can still be asked: whether there is evidence that the same rock eroded in the same way, whatever the rate, within the Sphinx enclosure itself. Another geologist, Colin Reader, investigated this question in 1997-98. The continuity of individual strata between the Sphinx and the enclosure walls was documented in detail by Lal Gauri as part of Lehner's 1979 survey of the Sphinx, so there was no question there about whether rock strata could be compared.
Reader found that the rock strata on the rear third of the Sphinx did not show the same weathering as the continuation of these strata on the more deeply eroded enclosure walls opposite them, and he found that the south enclosure wall had also eroded more deeply in a lateral direction (to the west). These findings strongly suggest that rainfall runoff from the plateau behind the Sphinx was the cause of erosion on the walls. The Sphinx itself could not erode from runoff because it was separated from the plateau by open space. These observations cannot be explained by other causes, such as wind or chemical effects, which should have affected the same rock in the same way on both the Sphinx and the walls.
Schoch and West had drawn attention to runoff as the likely cause of erosion on the enclosure walls as early as 1992. Reader confirmed and extended this observation by comparing the erosion of the same strata on both the walls and the Sphinx. Although Reader began circulating an unpublished paper on his findings in mid-1998, Lawton and Ogilvie either did not get it in time or did not choose to include it in their chapter.
The plateau behind the Sphinx was a catchment for rainfall and its runoff prior to the building of the three great Pyramids at Giza in the 2500s and 2400s BCE. The excavation of the plateau for stone to build the Khufu Pyramid drastically reduced this catchment area. Khufu preceded by several decades Khafra, the king who in the conventional view built the Sphinx c. 2500 BCE. Reader concluded that the excavation of the Sphinx enclosure must have preceded the Khufu Pyramid by some time in order for the enclosure walls to have eroded as deeply as they have from plateau runoff. This does not dispense with uncertainty about rates of erosion. But Reader disposes of the alternative weathering theories that have been proposed as the major causes of weathering in the enclosure, and he makes a strong case for the excavation of the Sphinx enclosure before Khufu.
One important point needs also to be made about Reader. He suggests dating the Sphinx about three centuries before Khufu. Since the publication of their book, Lawton and Ogilvie have revised their views to take account of Reader's geological observations and they have embraced Reader's dating. However, Reader gives no geological reason for arguing that the Sphinx is only 300 years older. His dating rests on the fact that archaeological context for large stone building can be found in Egypt that far back. He does not ask if the rainfall of 300 years was sufficient to produce the erosion he documents. Even given the uncertainty about rates of weathering, it is geologically unlikely that the rock weathered this rapidly over a mere three centuries. At minimum, I think, the enclosure must be dated well into the fourth millennium, when Holocene rainfall was much greater than in the diminishing centuries after 3000 BCE. An even earlier date is also possible.
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