
Mount Elgon, Uganda.
3″ long
Mount Elgon is an extinct shield volcano situated on the border between Kenya and Uganda. It is the oldest and largest solitary volcano in East Africa, covering an area of around 3500 km² (map). The nepheline tuff-beds on the lower slopes of the mountain are fossil-bearing and yield distinctive fossil wood. These layers of volcanic agglomerate out-crop in caves on outliers of the mountain, such as Walasi Peak on its western side. The petrified wood is particularly interesting material as it marks the onset of renewed activity after a quiet period in the volcanic history of Mount Elgon. Natrolite, Calcite and naturalist minerals have replaced the wood tissue. The mineralized wood fragments are all that is left of the ancient forests that clothed the dormant volcano. Their age is indeterminate; but the fossils are at least pre-Pleistocene in origin. The topography and geology of Mount Elgon, and the petrography of its lavas, have been described by Odman (1930) and more background on the fossil wood from this locality can be found in a series of papers by Bancroft (1932-1935). Nowadays, the area is protected by two National Parks (one on each side of the Uganda-Kenyan border). The Sipi River rises on the upper slopes of Mount Elgon before cascading down the foothills over 7km to form a series of four pretty waterfalls culminating in a 99m drop at an altitude of 1,775m outside the small trading centre of Sipi, 60km from Mbale by road. The most popular walking trail, only 20 minutes in each direction, leads from behind the post office in Sipi trading centre to the base of the main waterfall, where a small entrance fee is levied. If you choose, you can continue along this trail for another 20 to 30 minutes to reach a cluster of caves on the cliff above the river.
The largest of these caves extends for about 125m into the rock face, and contains rich mineral salt deposits that have clearly been worked extensively at sometime in the past, as well as traces of petrified wood. Walking back to the trading centre from the caves along the main road, you’ll pass the top of the main waterfall, as well as an important local shrine set within a small forest-fringed cavern.