224 NATURAL SCIENCE [April 



group have been elevated, and since their elevation have, like the 

 northern part of Queensland, remained nearly stationary and ex- 

 posed to great and prolonged denudation and erosion, which has 

 reduced the islands to their present height ; the platforms upon 

 which the barrier-reef corals have grown being merely the flats 

 left by the denudation and erosion of a central island of greater 

 size than that now left ; while the atolls are similar flats from the 

 interior of which the islands have been eroded and the lagoons of 

 which have been continually scoured by the action of the sea, the 

 incessant rollers pouring a huge mass of water into the lagoon, 

 which finds its way out through the passages leading into it." In 

 short, the Fijian area is one of elevation and not of subsidence, 

 though what the age of the elevated reef may be is uncertain. 

 Since it attains a thickness of 800 feet, it was very probably de- 

 posited originally during the period of subsidence, but this has 

 nothing to do with the present shape of the atolls. Prof. 

 Agassiz, who is informed by Prof. David that the evidence of 

 the Funafuti boring was not so simple as was at first supposed, 

 suggests that the boring merely penetrated the base of an ancient 

 reef, and therefore in no way corroborates the theory of a sub- 

 sidence. Prof. Agassiz is also inclined to ascribe the formation of 

 atolls more generally than has hitherto been done to the erosion 

 of volcanic summits or of extinct craters. He describes one or two 

 undoubted cases in the Fiji group, and points out that many of the 

 smaller atolls may have been formed in the same way. The great 

 depth of the lagoons of some of the atolls is quite as intelligible 

 upon this view as on the theory of subsidence. All interested in 

 coral reefs will look forward to the fully illustrated report of his 

 cruise which is promised by Prof. Agassiz. 



A Note on Plant Distribution 



We recently received a number of a bi-monthy French journal, pro- 

 bably unknown to most of our readers, the Bevue des Sciences 

 Naturelles de VOuest (vol. vii., No. 2), which contains the second 

 and concluding part of an account of the genus Acaena by M. P. 

 Citerne of Nantes. Acaena is a genus of Eosaceae, very closely 

 allied to Poteriiwi, two species of which, F. Sanguisorha (Salad 

 Burnet) and P. officinalis (Great Burnet), are well-known members of 

 our British flora. It resembles PoUrinm in habit, containing about 

 forty species of small low-growing herbs or under-shrubs. Poterium 

 is a north temperate plant ; Acaena, on the other hand, is widely 

 spread over the southern hemisphere, advancing in America as far 

 north as Mexico. Associated with its occurrence over so wide an 

 area we find an interesting means for distribution in the structure 



