“My first occupation [writes Speke][56] was to map the country. This is done by timing the rate of march with a watch, making compass bearings along the road, or any conspicuous marks,--as, for instance, hills off it,--and by noting the watershed,--in short, all topographical objects. On arrival in camp every day came the ascertaining, by boiling-point thermometer, of the altitude of the station above the sea-level; of the latitude of the station by the meridian altitude of a star taken with a sextant; and of the compass variation by azimuth. Occasionally there was the fixing of certain crucial stations at intervals of sixty miles or so, by lunar observations ... for determining the longitude, by which the original-timed course can be drawn out with certainty on the map by proportion.... The rest of my work, besides sketching and keeping a diary, which was the most troublesome of all, consisted in making geological and zoölogical collections. With Captain Grant rested the botanical collections and thermometrical registers. He also undertook the photography. The rest of our day went in breakfasting after the march was over,--a pipe, to prepare us for rummaging the fields and villages to discover their contents for scientific purposes,--dinner close to sunset, and tea and a pipe before turning in at night.” Speke noticed in Uzegura deposits of pisolitic limestone in which marine fossils are observable. He draws attention to the interesting fact that a limestone formation occurs with a few breaks almost continuously from the southwest coast of Portugal, through North Africa, Egypt, and part of the Somali country, across Arabia to eastern India.[57] In connection with this it may be mentioned as a point of great interest that Mr. C. W. Hobley (Sub-Commissioner in the East Africa Protectorate) discovered deposits of limestone in the Nyando valley, about forty miles from the northeast corner of the Victoria Nyanza.