300 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



8 miles off shore at Progreso, and in these he found only two fragments 

 of coral, the main mass of the samples being shell fiagments. 



HONDURAN REEFS. 



Although this is an important barrier reef, its length being 125 

 sea-miles, I know of no adequate published description ol it, nor oi 

 any published account of the shore line or of the oscillations of the 

 strand line behind it. The configuration ol Honduras Bay and of 

 the Gulf of Dulce, which lies inland from it and is connected with it 

 by a waterway, as well as that of Chetumal Bay, points clearly to 

 submergence. The reef occupies the outer edge of a platform 10 to 

 22 miles wide and is separated from the shore by a channel from 11 

 to 33 fathoms deep. This is a remarkably continuous barrier reef, 

 but it shows discontinuity at its southern end and therefore evidence 

 of superposition. 



MOSQUITO BANK. 



Hayes, although he was not giving particular attention to coral 

 reefs, has made one of the finest studies of a shore line in a coral- 

 reef area as yet published.^ The following is quoted from his 

 article:^ 



7. In middle Tertiary time the region was elevated and subjected to long-continued 

 subaerial degradation, and the narrower portion of the isthmus was reduced to a pene- 

 plain, with monadnocks at the divide near the axis. There is no evidence that open 

 communication has existed between the two oceans across this portion of the isthmus 

 since the middle Tertiary uplift. 



8. In post-Tertiary time the region was again elevated and the previously developed 

 peneplain deeply trenched. 



9. A recent slight subsidence has drowned the lower courses of the river valleys, 

 and the estuaries thus formed have subsequently been filled with alluvial deposits. 



J. E. Spurr furnished me a note ^ confirming Hayes's deduction 

 regarding the submergence of the lower courses of the streams on 

 the east coast of Nicaragua. Subsequently I had profiles drawn 

 across Mosquito Bank (see text fig. 11, page 275).'' These indicate 

 submergence to an amount of about 20 fathoms. As on Mosquito 

 Bank there is a submerged terrace front between about 20 and 25 

 fathoms in depth, the bank had to exist previous to formation of 

 that feature, and as the living reefs grow on the shallower flats, 

 which according to available evidence was out of water during at 

 least a part of Pleistocene time, they are necessarily superposed on 

 an antecedent basement. Furthermore, the enormous area of the 

 flat and the relatively small areas occupied by hving reefs, lead to 

 the same conclusion — that is, the living reefs are merely growing on 

 parts of a submarine plateau where conditions favor their life. 



1 Hayes, C. W., Physiography and geology of region adjacent to the Nicaragua Canal route, Geol. Soc. 

 Amer. Bull., vol. 10, pp. 285-348, pis. 30-32, 1899. 



2 Idem, p. 348. 



3 Amer. Geog. Soc. Bull., vol. 46, p. 429, 1914. 



* Wash. Acad. Sci. Journ., vol. 6, pp. 57, 62, 1916. 



