340 Miscellaneous, 



the two formations has already been pointed out by Langenbeck *, 



who has also endeavoured to show that Guppy's theories are unten- 

 able. 



As regards the more special study of the reefs, I have chiefly 

 devoted my attention to determining the way in which the reef^ are 

 composed of the various forms of corals, how the latter are distri- 

 buted upon the reefs, and what is the nature of the bottom upon 

 which they rest. I cannot here enter into details, but would lay 

 special stress on two points only. The observation has already been 

 noted in various (piarters, that Stony Corals may be temporarily de- 

 prived of Avater and exposed to the sun and the open air without 

 perishing. I made precisely the same discovery upon the reefs near 

 Dar-es-Salaam. Certain forms (Porites, Ooiiiastrcva, Coeloria, Tu- 

 hipora) lie for hours during the ebb-tide, which is a very low one 

 in that region, freely exposed to the air, but live and thrive exceed- 

 ingly. That this faculty is wanting in other forms is shown at 

 once by the fact that a number of species are met ■with in the com- 

 pany of those mentioned above, at the same altitude of the reef, but 

 are there found only in holes and pools, so that the}' are always 

 covered by water. 



The following observation is also important. I found at certain 

 points of the reefs near Dar-es-Salaam extensive banks of living 

 corals, resting upon a foundation wliich was quite loose. The latter 

 consisted of detritus (sand and gravel), which was held together by 

 sea-wrack, and in this wrack were numerous corals, some of wliich 

 were of but little thickness, while others formed large blocks, of 

 which, moreover, entire banks were composed. All these blocks 

 lay loose upon the bottom ; I was able, provided their weight was 

 not so considerable as to offer resistance, to lift them up or roll them 

 over with ease. This observation is interesting in so far as it has 

 been maintained by J. Walther (loc. cit.), that coral-reefs could only 

 become established upon a firm (rocky) bottom; which may, indeed 

 be correct enough so far as regards the forms mentioned by him 

 (the umbrella-shaped Madrepores). There are, nevertheless, forms 

 of corals (1 am here alluding to species of the genera PMmmocora, 

 Monti-pora^ and Lophoseris) which are capable of thriving upon a 

 looser bottom in large blocks and forming banks. Such banks may 

 then again furnish a basis for other corals. 



In accordance with tlie negative shore-displacement I also found 

 an old coral-bed above the present level of the sea. The one which 

 I examined in sit a is of quite recent date, yet older raised beds of this 

 kind doubtless occur in the region in question. The coral structure 

 is for the most part no longer recognizable in the fossil beds. 



The coral-fauna of Par-es-Salaam is closely allied, as might at 

 once be conjectured from its geographical position, to that of the 

 Red Sea (cf. Klunzinger). Yet we here already find a few Pacific 

 types, which are wanting in the lied Sea. — Zool. Anzii^jer, 

 XV. Jahrg., no. .'381 (Jan 1 1th, 1892), pp. 18-20. 



• liungenbock, ' Die TluMrimi iiber die Entstidiung dor Koralleninseln 

 &c.' : Leipzig, 1890. 



