Miscellaneous. 339 
On Coral-Reefs of the East-African Coast. 
By Dr. A. Orrmann, of Strassburg. 
Since the publication of a more detailed treatise upon the subject 
of my investigations into the coral-reets of the German Kast-African 
coast will still require some time, I venture to communicate herewith 
a brief account of the most important of the results which have been 
gained. 
The entire East-African coast-region, so far as I explored it, from 
Zanzibar southward to Mikindani, is one of negative shore-displace- 
ment. I was able to collect proofs of this at the most widely 
different spots ; just as, moreover, similar observations are already 
available for two localities (Zanzibar and Songa-Songa Isl.). It is 
probable that the same movement extends to the greater portion 
of the East Coast of Africa. 
The development of the coral-reefs also corresponds to this 
negative movement: they accompany the coast throughout and are 
true shore reefs (“* Strandriffe ”), Their horizontal extension in the 
direction at right angles to the coast is in close connexion with the 
slope of the sea-bottom from the shore-line to deep water. Where 
great depths are found close to the shore (which occurs in our 
territory chiefly in the south, near Lindi and Mikindani) there is 
only a narrow shore reef; but where the sea remains shallow to a 
greater distance from the coast (e.g.in the Mafia and Zanzibar 
Channels) not only does the shore reef attain a greater breadth, but 
also isolated reefs are found further outside. I term the latter 
SHALLOW-WATER REUEFS (“ Flachseeriffe ”). (J. Walther has adopted 
the name PELaGic REEFs for similar formations in the northern part 
of the Red Sea: cf. J. Walther, ‘“ Die Korallenriffe der Sinaibalb- 
insel,” Abh. K. sachs. Ges. Wiss. 24 Bd., 1888.) 
I was nowhere able to observe a formation of barrier-reefs or 
atolls, and after a careful study of the English Admiralty charts 
their occurrence appeared to me to be improbable, even at spots 
which I did not visit. As TRur barrier-reefs and True atolls I regard, 
be it well understood, only those which respectively exhibit a 
channel or lagoon of great depth and rise from very deep water. I 
am firmly convinced that formations of this kind can only arise in a 
region of positive shore-displacement, and that those cases are of 
rare and unusual occurrence in which they appear in stationary 
regions. In this respect, therefore, I abide by the old theory of 
Darwin and Dana, in opposition to the views recently published by 
Guppy, who would deduce the existence of negative shore-displace- 
ments from the actual presence of atolls. The very absence of such 
reef-formations in our territory is an indirect proof that in regions 
with negative shore-displacement atolls and the lke are not formed. 
1 regard the atolls of the Straits of Jubal in the Red Sea, which are 
figured by J. Walther (loc. cit.) not as TRUE atolls, in the sense given 
above, but as atoll-like formations, resulting from the peculiar peri- 
pheral growth of the corals, which can be observed on a small and 
large scale in every coral-reef. Moreover the difference between 
