478 Correspondence — Br. John Home. 



Feet. 

 1. Chamaheds 300 



300 



900 



1500 



30 



90 



30 



2. Pseudo-lagoon — (a) Sponges 



[b] Mussels, etc. 



(c) Heiiopora 



3. Clinker embankment (broken corals) 



4. Kock pools .... 



5. Outer zone, massive living corals 



A map and diagrams are given. The authors summarize as follows : — 

 The growth of an individual reef is shown to proceed in a regular 

 cycle. If the reef reaches the surface with its axis along the wind, 

 then its shape endures ; but if across the wind, then its extremities 

 are produced backwards, forming first a crescent, later a horseshoe, 

 and lastly an oval, thus enclosing a lagoon. Descent at this stage 

 arrests development or rejuvenates the reef. In quiescence the lagoon 

 walls broaden, the lagoon is obliterated with sediment, a vegetated 

 sandbank spreads on the summit, and the atoll, grown to a cay, has 

 arrived at maturity. ' Negro-heads ' are not, as has been advanced, 

 relics of former raised reefs, but masses of coral tossed up by hurricanes, 

 and no great antiquity can be ascribed to them. They find for Darwin's 

 view that this portion of the Great Barrier has been formed during 

 subsidence. 



COE.IlESi'OITIDEnsrCE. 



SUMMARY OF PROGRESS. 



SiK, — In the review of the Summary of Progress of the Geological 

 Survey for 1907 (August number, p. 379), two rather misleading 

 statements have been inadvertently made which it is desirable to 

 correct. It is stated that the Appendix contains articles " on the 

 Mugearites, one of the Tertiary igneous rocks of the Inner Hebrides," 

 and " on the marine beds near the base of the Upper Carboniferous in 

 Scotland." 



The article on the Mugearites was written to describe rocks of this 

 type occurring in the Carboniferous volcanic series in Midlothian and 

 East Lothian. The Tertiary Mugearites, previously recognised and 

 named by Mr. Harker, were only introduced for the sake of com- 

 parison. The marine beds referred to occur, not near the base of 

 the Upper Carboniferous in Scotland, but near the base of the Upper 

 Carboniferous red barren measures, which in Scotland overlie all the 

 worked coal-seams of the Coal-measures, 



J. HOKNE. 



DESOR'S " SYNOPSIS DES ECHINIDES FOSSILES." 

 Sir, — The "Synopsis des Echinides Fossiles," by E. Desor, is a work 

 still in constant use by every worker on the Echinoidea. Its use, 

 however, is rendered difficult, first, by the lack of an index — a want 

 particularly felt in these days when so many names have been altered; 

 secondly, by the fact that it was published in livraisons issued at 

 different dates, and that certain sheets were cancelled, others being 

 substituted at a later date. 



