Geology and Natural History. 241 



describes the Fishes taken within the lagoons and from fresh- 

 water pools. Of the latter only one (Barbus vitfatus Day) is a 

 true fresh-water form. The Marine Turbellaria, by F. F. Laid- 

 law, contains a systematic list of 15 species, 13 of which are 

 described as new, and many valuable anatomical notes are given 

 with about a dozen text figures and two plates ; the general 

 figures being reproduced in colors. Some new and valuable 

 deductions are given in conclusion and under " Natural History 

 Notes " many interesting facts are mentioned, especially in regard 

 to the collecting and preservation of material. k. j. b. 



Mr. Gardiner continues his discussion of the formation of coral 

 reefs and adds much that is new (pp. 313-346). He shows that 

 the coral sand rock is formed by twice wetting and drying of the 

 beach sand during the rise and fall of the tide. In the latter 

 process the salts from the sea-water are deposited on the sand 

 grains, many of which are redissolved by being covered by the 

 tide, but carbonate and sulphate of calcium remain and fill the 

 interstices of the sand, binding them together. The sulphate 

 becomes replaced by less soluble carbonates and the rock ulti- 

 mately formed of nearly pure carbonate of lime, the rock naturally 

 being built from the surface downward. In nearly all cases the 

 slope of the mass is that of the beach and becomes of great den- 

 sity and hardness as it is more and more indurated with carbonate 

 of lime. From the study of such masses off any island the former 

 extent and contour of the land may be deduced with considerable 

 certainty. " The erosion of land in the Maldives, the formation 

 of flats at about the low tide level by washing away of the land 

 and hollowing out of such flats to form first pools, then velu or 

 definite lagoons, may absolutely be traced." 



In regard to the formation of lagoons Mr. Gardiner says : 

 " In conclusion, it is a fair deduction that the increase both in 

 depth and extent in the lagoons of the Maldive atolls is mainly 

 due to solution, an important additional factor being the outwash 

 of fine matter by the tidal and oceanic currents. It is obvious, 

 though, that there are two nicely balanced sets of conditions, 

 causing the filling in or increase in size of any lagoon." 



The bathymetrical limits of various species of reef-building 

 corals has been determined. "Darwin in placing the extreme 

 depth of flourishing banks of surface-red corals at 25 fathoms 

 was entirely correct. The specimens of these corals procured 

 from beyond this depth show clearly in their growth that the 

 increased depth is deleterious to them. At the same time the 

 presence of a series of other genera of corals, which evidently 

 flourish just beyond where the surface forms cease to exist, 

 although with a considerable range in depth, is for the first time 

 clearly demonstrated." 



Mr. Gardiner had unusually favorable opportunities for study- 

 ing the rate of growth of reefs and reaches a conclusion widely 

 different from Dana's, who considered five feet in 1000 years an 

 average. " Considering all the various factors, and particularly 



