Extension of the Karroo Lavas. 169 



basalts and are probably anything from 500 to 1,000 feet in thickness. 

 They have a gentle easterly dip, and the directly underlying rocks are 

 very badly exposed ; in fact, the sandstones seen to the west are on 

 a horizon which is probably at least 500 or 600 feet below the base 

 of the flows. They are nearly white felspathic grits, extremely 

 similar to the Upper Sandstones of the Wankie Coalfield in Southern 

 Rhodesia, but they clearly belong to a higher stratigraphical horizon, 

 as they are certainly 1,000 feet above the Coal Shales. Above the 

 basalts are sandstones of an entirely different character, very like 

 some of the New Red rocks in England. They are no doubt of 

 Jurassic age, and are about 1,200 feet thick, being succeeded by 

 the Lupata Volcanics, which must be of Lower Cretaceous age, if, 

 indeed, they do not reach down into the Jurassic period. It should 

 be noted that the isolated sheet of columnar rhyolite which caps 

 the magnificent scarp at the entrance to the gorge divides tlie sand- 

 stones almost equally into two divisions. These may be termed the 

 Upper and Lower Lupata Sandstones for convenient reference. 

 They are very varied in character, ranging from coarse con- 

 glomeratic varieties to what may be termed " marls ", but are chiefly 

 coarse to medium sandstones red, purple, brown, yellow, or even 

 occasionally white in colour. The Lupata Volcanics are entirely 

 different from any of the Karroo lavas. As a field term " felspar- 

 porphyry " may be applied to most of the varieties, but some of, 

 the rocks are rhyolitic, while others contain large porphyritic 

 nepheline crystals (often rej^resented on weathered surfaces by 

 cavities), and at two localities specimens were secured which contain 

 numerous porjohyritic crystals which must be leucite or pseudo- 

 morphs after that mineral. Tuffs and agglomerates occur at intervals 

 and also seams of tufaceous sandstone. The volcanics are overlain 

 by the Cretaceous sandstones, which often show pebbles of the 

 characteristic Lupata Volcanics, and are themselves succeeded on 

 the Sheringoma plateau by limestones containing numerous fossils 

 which range from Late Tertiary to Upper Cretaceous age. The, 

 thickness of all these strata is very great, and it is hoped to describe 

 them in more detail when the petrographjcal and palseontological 

 collections are worked up. They are referred to chiefly to emphasize 

 the fact that to attribute all the nepheline-bearing rocks of East 

 Africa to the Tertiary period is clearly erroneous, as the Lupata 

 Volcanics cannot by any possibility be higher up in the strati- 

 graphical scale than Lower Cretaceous. No faulting can be invoked 

 to invalidate the stratigraphical evidence, owing to the fortunate 

 fact that, as already mentioned, the overlying Cretaceous rocks 

 contain pebbles derived from the volcanics adjacent to them. 



II. Maringwe Area. — If the inland district of Maringwe be 

 approached from the north side, i.e. from the Zambesi, or from the 

 east, as, for instance, from Inyaminga, the gently inclined Cretaceous 

 sandstones of Sena in the one case, or the Tertiary limestones in the 

 other, are gradually found to give way to older and older sediments 



