Ee, 
Note on Dr. Donaldson Smith's Geological Collection. 
By jew. -Greeory, Disc, F.G,S. 
Dr. DONALDSON SMITH’s energies having been mainly devoted 
to geographical and zoological work, his geological collection 
is small. It consists of eight rock specimens, one fossil brachi- 
opod, a broken lamellibranch, and some fragments of ammonites. 
The ammonites are named in a list by my colleague, Mr. G. C, 
Crick. The other specimens are as follows : — 
1. Coarse, weathered trachytoid phonolite. Locality, Marsa- 
bit. September, i895. 
2. Pumiceous trachytoid phonolite. From Marsabit. 
3. Compact trachytoid phonolite, with pilotaxitic structure. 
Marsabit, September, 1895. 
4. Weathered brown tuff associated with last. At Marsabit. 
September, 1895. 
5. Trachytic (or phonolitic) brown weathered tuff from one 
hundred feet above level of Marshy Lake in Omo 
valley. 
6. Broken lamellibranch (#¢theria, sp. ?) from alluvial deposits 
in Omo valley. 
7,8,&9. Archzan gneisses, crowded with epidote. Shores 
of Lake Rudolf. 
10. Rhynchonella subtetrahedra, DAV. 
Though this collection is small, it is sufficient, taken in connec- 
tion with what is known of the adjoining areas, to throw consider- 
able light on the geological structure of the country traversed by 
Dr. Donaldson Smith, and on the extent of the range of the two 
principal East African rock series. 
As I have recently shown elsewhere,! the geological formations of 
East Africa may be divided into four main divisions; 1. A series 
of gneisses and schists referable to the Archean series; 2. Some 
1 J. W. Gregory, The Great Rift Valley. London, 1896. pp. 213-236. 
