130 dk. r. Oswald ox the [June 1914* 



of sedimentation to be observed anywhere in the series, although 

 -changes in character are frequent : — 



(1) An upper series (average thickness = 70 feet) of grey and brown clays 



and shales, containing very few fossils. Beds of sandstone are of rare 

 occurrence. 



(2) A middle series (average thickness = 30 feet) of variable red and grey 



clays, with white sandstones in the lower half. 



(3) A lower series (average thickness = 55 feet) of buff-coloured sandstones 



and torrential gravels (containing the Dinotherium Zone), passing down 

 (at Nira) into clays and marlstones. 



Travertinous beds occur at intervals throughout the whole 

 series. 1 The exposures are in gullies and cliffs at Nira, Kachuku, 

 and Kikongo, to the east of Karungu (see PI. XXVI, and § III 

 on the Distribution of the Miocene Series, p. 135). 



(1) The upper series (Beds 1 to 12) forms a natural division, 

 consisting mainly of pale-grey, sometimes brownish-grey clays, 

 which frequently alternate with thin seams of shale (often with 

 dendritic manganese oxide). Chiefly in the upper part (for 

 instance, Nos. 3, 5, & 8, but also No. 11 at South Nira) beds of 

 grey, fine-grained, argillaceous sandstones occur, usually current- 

 bedded — generally about 3 feet thick and exceptionally (No. 3 

 at East Kachuku) 10 feet thick (see PL XX). They are composed 

 of quartz-grains, large plates of biotite, and augite-crystals. 



Fossils are extremely rare in this upper series, and usually occur 

 only in the sandstones ; for instance, a few land-shells in No. 8 

 (Tropidopliora nyasana E. A. Smith, Limicolaria, Cerastus). an 

 Ampullaria and a crocodile's tooth in No. 5, and an indeterminable 

 river-crab and some Crocodilian scutes in the clay of No. 12 at 

 Nira. At the very top of the series, immediately below the capping 

 of nepheline-basalt, the grey clay of No. 1 contains portions of 

 calcified tree- trunks ranging up to 1 foot in diameter and 1| foot 

 in length, of Dicotyledons. They have been examined under the 

 microscope by Miss N. Bancroft, who finds that the specimens 

 represent types belonging to the Malvaceae (similar to the African 

 Bombax insigne), to the G-eraniales (Sumiria), to the Papilio- 

 nales, and to the Caprifoliacese (similar to some species of Lonicera 

 and Viburnum'). Since one of these stems, in the same state of 

 mineralization, occurred embedded in the lower brecciated portion 

 of the basalt- flow at Kachuku, it seems probable that they had 

 been fossilized by the agency of calcareous springs at the time of 

 the deposition of the grey clays, and before the eruption of the 

 basaltic lava-flows. 



Thin beds of travertine alternating with grey clay are character- 

 istic of the horizon of Nos. 9 & 10 in the eastern area, but do not 

 occur at Nira in the extreme west. 



Immediately below the sandstone of No. 8 at Kikongo, in the 

 extreme east of the area, a breccia (1 foot thick) occurs of coarse 



1 The detailed measurements and descriptions are given in the comparative 

 table of the outcrops exposed in the various gullies, Appendix I. 



