James Harrell responds to Robert Schoch
From “Readers’ Forum”: KMT Vol. 5, No. 3, Fall 1994, pp 3-4
Reproduced with Permission
In the summer 1994 KMT (“The Sphinx Controversy – Another Look at the Geological Evidence”), I examined the arguments presented by geologist Dr. Robert M. Schoch for a pre Neolithic age for the Great Sphinx of Giza (see his article in the summer 1992 KMT). His principal evidence for this astounding claim is the deep weathering suffered by this monument since it was carved from the limestone bedrock. I concluded that the observed weathering is entirely consistent with a Fourth Dynasty age. In the same issue of KMT, a letter by Schoch was published which criticized my re-interpretation of his evidence and it is this letter that I am responding to here.
Schoch’s main objection was to my suggestion that for most of its existence the Sphinx has been buried to its neck in sand that was kept wet much of the time by rainfall and Nile floods. He questions the wetness of the sand cover but does not say why it should have stayed dry. Schoch next offers four observations that he says invalidate the wet-sand hypothesis:
(1) If the effects of a wet-sand cover are so deleterious, he asks, then why is the same kind of undulated weathering pattern seen on the Sphinx (which he attributes to rain-induced erosion) not found on the rock-cut tombs and other structures nearby to the south, given that they also occur in the same strata and at the same elevation as the Sphinx? In point of fact, these structures are a few meters higher than the base of the Sphinx (and thus beyond the reach of the Nile floodwaters) and are carved in the most durable of the Sphinx beds (primarily those of the neck and head). Schoch implies that these structures exhibit only the flat profiles he attributes to wind erosion. He is only partly correct.
Undulated weathering profiles are seen on the exposed walls in the part of the Khufu/Khafre quarry between the Sphinx and the Fourth Dynasty Khent-Kawes monument, 220 meters to the southwest. The relief on these profiles is less pronounced than those found on and around the Sphinx; but this is to be expected, given that the quarry walls are situated at a higher elevation and consist of limestone from the upper, more durable Sphinx beds. Significantly, the exteriors of the Old Kingdom tombs on the north side of the Khent-Kawes monument show this same type of weathering profile. The fact that the original flat profiles of some tombs are preserved can probably be attributed to differences in exposure and limestone durability. It has, however, been suggested by others that flat and undulated profiles may be related, respectively, to abrupt and gradational changes in limestone lithology. More field work is need to evaluate this possibility.
(2) Schoch cites as decisive evidence against the wet-sand hypothesis the fact that the most durable limestone beds – which occur at the top or me Spninx enclosure on the south and west walls – are worn back more than the underlying, less durable beds. He says this could only have happened through erosion by rain-runoff cascading over the walls. In this he cannot be more wrong. The walls of the Khufu/Khafre quarry, of which the Sphinx enclosure is a part, were originally cut (battered) with a slope of roughly eighty degrees. This can be seen, for example, at the Khent-Kawes monument and also in the southeast comer of the Sphinx enclosure, where the wall is not deeply weathered. Furthermore, it is to be expected that the tops of the enclosure walls would have been worn back over the millennia as a result of: (i) numerous ancient and modern episodes of sand removal from the Sphinx enclosure; (ii) construction of the Khafre causeway on the south side; (iii) limestone quarrying on the east side; (iv) foot traffic of countless thousands of ancient and modern visitors; and (v) encasing the Sphinx with blocks of limestone during the reigns of Thutmose IV in the Eighteenth Dynasty. It may well be that much of the wear occurred during this latter event, when limestone blocks were brought down the Khafre causeway from this king’s pillaged mortuary temple and lowered (?) into the Sphinx enclosure from the tops of the southern and western walls.
To all of this can be added the observation that, contrary to what Schoch has claimed, the enclosure walls do not conform well with what one would expect from erosion by rain runoff. Only if the limestone beds are of similar durability from top to bottom would the upper beds be worn back preferentially. If, on the other hand, the upper beds are more durable than the lower beds – as is the case in the Sphinx enclosure – then the lower beds should be preferentially eroded and therefore overhung by the upper beds (a classic example of this type of differential erosion is the Niagara Falls.
(3) Schoch says that the deeply weathered fissures cutting the Sphinx and enclosure walls cannot be explained by the wet-sand hypothesis. I agree and I did not say otherwise in my article. These features are tectonic joints that developed in the limestone bedrock of the Giza Plateau millions of years ago and have since been enlarged through dissolution by circulating subsurface waters. Such fissures are a common feature of limestones throughout Egypt and have absolutely no bearing on the age of the Sphinx.
(4) Schoch says that if the Nile flood actually reached the elevation of the Sphinx, as I have claimed, then the bases of this monument and the enclosure walls should have been undercut by the erosive action of floodwaters. He is wrong, however, in thinking that this should be the result. Firstly, the river would reach the level of the Sphinx during the slackwater conditions existing at the flood maximum and so would have little or no erosive force. And, secondly, the Sphinx would have been covered by sand and so the only effect of the flood would have been to allow water to infiltrate the sand.
Schoch reiterates his view that the low-velocity layer in his seismic profiles corresponds to a weathering zone. He says, simply, that he has “good reason to believe” that this is the case,” but he declines to share his reason with the reader. The only way this issue can be resolved is by drilling through this layer and extracting a core. It is unlikely, of course, that this could ever be allow by the Egyptian antiquities authorities. Schoch asks why the base of the low-velocity layers does not show an eastward dip if it corresponds, as I claim, to the “shoal reef facies” of the Mokattam limestone. In my article I said this layer probably represents only the upper part of this facies, where large coral colonies are abundant. These colonies are irregularly distributed and decrease gradually in abundance downward. There is thus no reason to expect that the base of the low-velocity layer would closely conform to the local dip.
Although I believe a wet-sand cover would hasten the disintegration of limestone in and around the Sphinx, such a cover is not required to explain all the observed weathering. Archaeologists and geologists working at the Sphinx during the last two decades have observed that the exposed limestone is spalling off at an alarming rate. It seems a mere century of such activity would leave an originally smooth-surfaced Sphinx deeply weathered. While some of the recent weathering can be attributed to air pollution and other factors related to the urbanization of the Giza area, most of it certainly cannot. In any case, it is obvious that the Sphinx limestone has a propensity to weather rapidly, given the right conditions.
Most of the weathering of the Sphinx may have taken place during the 1,100 years between its carving by Khafre and its encasement by Thutmose IV. This is apparent from the fact that the casing was carved to fit into already deeply recessed beds in the Sphinx. The effect of the casing would have been to retard the weathering by keeping the wet-sand cover away from the limestone bedrock.
The 4,500 years since Khafre’s reign are clearly more than enough time to deeply weather the limestone of the Sphinx and enclosure walls, and it seems ludicrous for Schoch to claim that many thousands of more years are needed to accomplish the task. All things considered, I am convinced that a Fourth Dynasty date for the Sphinx is the most sensible and best-supported interpretation of the geological evidence.
Dr. James A. Harrell
The University of Toledo