374 SCIENCE PROGRESS. 



The earlier explorers, such as Lyon (5), and Denham and 

 Clapperton (6), lived before the days of modern geology. 

 It is true that Lyon's specimens were examined by Buck- 

 land (5, pp. 361-369), and Denham's by Konig (6, pp. 247- 

 261) ; but the specimens were too few and the state of the 

 science too imperfect to allow of any but erroneous con- 

 clusions. In more recent years, misfortune has attended 

 the footsteps of two at least of the few who have been 

 qualified to make geological observations. The French 

 geologist, Roche, perished in the massacre of the ill-fated 

 second expedition under Flatters ; and Overweg, the com- 

 panion of Richardson and Barth, fell a victim to the climate 

 of the shores of Lake Tsad. 



We are compelled then to rely, to a considerable extent, 

 on scattered observations made by travellers who devoted 

 themselves chiefly to other matters ; and if it were not that 

 the structure of the region is singularly simple, the geology 

 of the Sahara would be almost unknown. But the imper- 

 fect notes of these explorers serve to fill in the gaps left 

 between the fuller observations of more skilled geologists ; 

 and it is possible, as Rolland and others have shown, to 

 form a picture of the geological structure of the whole 

 region. No doubt such a sketch as our present materials 

 allow, will be faulty, and undoubtedly it must be incomplete ; 

 but it cannot be entirely devoid of interest, and if its 

 imperfections be borne in mind, it may not be without 

 its use. 



Pomel (7) was the first to attempt a general description 

 of the geology of the Sahara ; and although our knowledge 

 is wider now, his account is still of value. More recently 

 Zittel (8) and Suess (9) have endeavoured to collect and 

 harmonise the geological notes of travellers in these 

 regions; and within the last few years Rolland (10, 11) 

 has applied himself to the same task. 



The explorers to whom these writers look for the 

 principal part of their facts are Lenz (12) in the Western 

 Sahara, Roche (13, 14) and Rolland (15) in the Algerian 

 Sahara, Overweg (16, 17) in Tripoli and Fezzan, and 

 Zittel (8) in the Libyan Desert. The accounts of these 



