484 
THE GEOLOGICAL HISTORY 
belong to a Mediterranean fauna, and doubtless reached East 
Africa from the north. The fossils in the upper Cretaceous 
deposits of Mozambique, which were laid down at the same 
time as the English Chalk, are allied to those of southern 
India, and indicate that the sea in which they lived invaded 
East Africa from the south. These Mozambique fossils 
further show that a land connection still existed between India 
and East Africa — probably along the line of the Seychelles 
and Maldives. 
The Jurassic rocks were laid down quietly on the bed of 
the sea, and their deposition was undisturbed by volcanic 
eruptions ; but the more active earth movements in late 
Cretaceous times, and the foundering of the floor of the Indian 
Ocean between East Africa and India, led to volcanic out- 
breaks in western India on a colossal scale. 
These eruptions discharged the lavas (basalts and trachytes) 
known as the ‘ Deccan Traps,’ which cover over 200,000 
square miles in western India, and perhaps an equal area now 
buried in the Indian Ocean. The age of the eruptions is 
fixed as Upper Cretaceous (Upper Senonian and Danian) by 
the fossil frogs found in the old lake beds, preserved among 
the lavas in Bombay, and by the shells of the Pab beds. 
If the formation of the Arabian Sea led to such violent 
volcanic activity in India, it is natural to expect some 
corresponding events in East Africa, on the other side of the 
foundered land ; and the beginning of the volcanic period in 
East Africa may prove to have been simultaneous with that 
of India. 
The oldest modern lavas in eastern Africa appear to be 
those of the Athi and Kapiti Plains ; they consist of a rock 
named phonolite, as thin slabs of it give a clear musical note, 
and are used for rock harmonicons. Its chemical characteristic 
is its richness in soda. Mount Jombo, south-west of Mombasa, 
consists of igneous rocks which are apparently intrusive in 
the Jurassic beds ; and if so, they are not earlier than the 
Cretaceous. These Jombo rocks, I described, years ago, from 
specimens collected by Mr. Hobley, as nepheline-syenites, and 
they have strong chemical affinities to the phonolites. 
The phonolite of the Kapiti Plains is clearly of considerable 
