New Excavations at the Middle Stone Age Cartwright's site, Kenya

New Excavations at the Middle Stone Age Cartwright's site, Kenya

The Middle Stone Age (MSA) is significant inhuman evolution as it marks the beginning of modem human behavior. This includes symbolism, self adornment, trade networks and regional differentiation in technology (McBrearty and Brooks 2000).These developments may coincide with the emergence of our species, Homo sapiens. The term MSA was coined by Goodwin and Van Riet Lowe (1929)for stone tool complexes that did not contain characteristic Early Stone Age (ESA) tools such as hand axesnor typical Later Stone Age (LSA) ones such asmicroliths. The MSA is found inter-stratified between the ESA and LSA at numerous sites in Africa. While the term was initially invented for southern African archaeological material, it was soon realized that differences existed even here. Goodwin and Van Riet Lowe (1929) proceeded to divide the material into "industries" and "variations". Thus came into existence the terms Still bay Industry, Glen Grey Industry, Pietersburg Variation and Howieson's Poort Variation, among others (Vogelsang 1998; Kleindienst1967). Some of these terms persist while others have fallen from use. Other MSA industries in Afiica include the Lupemban in East-central Africa (Clark1970,1988; McBrearty 1 992), and the Aterian, and Nubian Complex in Northern Africa (Kleindienst2000; Van Peer 199 1).Cartwright's site (GsJj 75)GsJj 75 lies on the Kinangop plateau between the Aberdare ranges and the Rifi valley, over looking Lake Naivasha (0' 35' 50" S, 36' 27' 30" E) at anelevation of 2420 m. The Malewa River and its two tributaries, the Kitiri and Turasha Rivers drain theplateau. The vegetation was predominantly tussock grassland during Quaternary times but modem farming activities have altered the landscape to include pasture grass and exotic trees (Hamilton 1982;Bemun and Njoroge 1999). GsJj 75 is an MSA site attributed to the pseudo-Still bay industry by Leakey(1931), and dated to 440 ka (Evernden andCurtis1965). This date has not been generally accepted, largely because the stratigraphic relationship of the sampled volcanic tuff and artifacts found at the site cannot be reconciled (McBrearty and Brooks2000). The site however remains an important focus for understanding the chronology of the MSA. The oldest securely dated MSA sites are >285ka old and are found in the Kapthurin Formation of Kenya(Deino and McBrearty 2002).The technology of MSA artifacts at GsJj 75,has not been adequately described. Cartwright's and Wetherill's (GsJk 12) sites are dated by 40K/39A(rP Otassiumargon) to 440 ka and 557 ka respectively.The ages of industries termed "Pseudo-Stillbay" andStillbay in Kenya are still unclear. These sites include GvJm 16, Malewa Gorge and Prospect Farm(Anthony 1967). The Pseudo-Still bay artifacts from GsJj 75 described by Leakey (I 93 1, 1936), housed at the National Museums of Kenya, include points, tools diagnostic of the MSA but they were from surfacecollections. Artifacts collected by Allen Turner in 1929 are also housed at the National Museum of Kenya in Nairobi but this collection is highly selected and comprised only of formal tools.  Preliminaty work on the Kiuangop plateau was carried out in two seasons of three weeks each in2001 and 2002 (Figure 1). In 2001, I surveyed the greater part of the North Kinangop plateau with the aim of relocating Cartwright's and Wetherill's sites and discovering new MSA sites. Wetherill's site was relocated but it had been destroyed by fanning activities. Cartwright's site was found to be in part intact and a controlled surface collection was carriedout in an area of 3 by 3 m (Figure 2). All 94 artifacts in this 9 m2 area were collected. Three rock shelters were also found in the vicinity of the site, two with LSA material on the slopes overlooking the Kitiri River and GsJj 77, located 800 m north west of Cartwright's site. The rock shelter GsJj 77, lies on the edge of the escarpment and contains LSA artifacts on the immediate slope. Fieldwork in the summer of 2002 focused on mapping Cartwright's site, measuring stratigraphic sections and excavating a geological trench (Figure2). Art&@ considered diagnostic of both the LSA and MSA lie on the eroded, gently sloping sm face. A stratigraphic sequence of 13 superimposed units was observed. With the exception of a paleosol, all are tuffaceow units (Figure 3). The paleosol is probably developed on a volcanic unit. Under low magnification, some tuff samples appear to contain feldspars, which are necessary for dating but further analysis is needed to ascertain if the tuffs are datable. Additional uncontrolled surface collections in 2002 were mostly carried out in the area 25 m northeast of geological trench ddl (Figure 2). This section of the site was fairly intact in 2001 but on returning in 2002, considerable erosion was found to have exposed more artifacts. However, slope collapse makes the stratigraphic origin of these artifacts difficult to determine. Many points were found but their provenience can only be established with further excavation. A large crescent was found here. A second crescent was recovered when clearing the slope of debris near geological trench. These large crescents recall those of the Mumba and Howieson's Poort industries that are found in terstratified within the MSA at Mumba, Tanzania (Mehlman 1989) and Klasies River, South Afiica (Wurz 1997). Crescents are part of the LSA tool repertoire and are thought to represent tool miniaturization attributed to specialization. Ambrose and Lorenz(1990), argue that microlithic elements in the MSA at Klasies River Mouth are an adaptation to scarce resources during cold and conditions. This model has not been tested for the Mumba industry. Geological trench ddl is 2 m by 5 m and reveals an occupation horizon consisting of a clayey paleosol containing artifacts. The paleosol has well developed root casts and a carbonate layer at its base(Figure 3). None of the artifacts appears to be rolled, and the presence of micro debitage <1 mm in width suggests that little disturbance has taken place (Schick1992). Several types of obsidian were observed among the artifacts and samples of obsidian debitage collected for geochemical analysis. Analysis of both in situ and surface material was carried out at the National Museum of Kenya laboratory in Nairobi. A total of 102 artifacts werere covered hm in situ context in the occupation horizon. Maximum artifact dimension averages 3.5 cm.None are larger than 6 cm and smaller class sizes are well represented (Figure 4). The 2002 excavated sample contains only 5 points, and 25 more were selected for analysis from the surtilce collection of Allen Turner housed at the National Museum of Kenya. Thirty pointed tools were analysed for symmetry, angle and intensity of retouch. Some points are symmetrical, bifacial, with flat invasive retouch and basal thinning indicating that they may very well have been hafted. Sub-triangular points with unifacial retouch are also present. While they have been retouched to an apex, they have steep angles and noninvasive retouch. A few points have serrated edges. Some points that are symmetrical, bifacially flaked with invasive retouch and have basal thirming qualify as projectiles. It can be argued that not all the tools that fit the definition of points were used as projectiles. Tools that have high retouch angles and are subtriangular may have been used as scrapers (see Wbdnath and Dibble 1994).