412 Prof. A. Agassiz. On the Formation of [Feb. 7, 



theory if time is allowed for them. The change at the G temperature 

 is the breaking up of a solid solution into a mixture of the compound 

 Cu 3 Sn and liquid, and is instantaneous : here we have a case of a solid 

 partially melting as it cools. 



The curve IKE'f forms with the part of the solidus immediately 

 above it an area, roughly triangular, within which all the alloys appear 

 to be uniform solid solutions, but, as soon as an alloy cools to the curve, 

 it becomes saturated and a new body crystallises out of the solid 

 solution. One branch of the curve 1XE'/ corresponds to the crystal 

 lisation of a body rich in copper, the other to the crystallisation of a 

 body rich in tin, which is probably the pure compound Cu 4 Sn. The 

 angle X (or rather C), is the eutectic angle at which both bodies 

 crystallise together, the whole phenomenon being exactly like 

 crystallisation out of a liquid. 



All the results obtained from the study of the chilled alloys are in 

 harmony with the pyrometric work of Koberts-Austen and Stansfield, 

 and many of the changes we have examined correspond to an 

 evolution of heat recorded by them. , 



The paper is an extension of a short paper published by us in the 

 'Proceedings' of December, 1901. 



On the Formation pf Barrier Reefs and of the Different Types of 

 Atolls." By Alexander Agassiz, For. Mem. R.S. Received 

 February 7 —Read March 19, 1903. 



The results here presented are based upon observations carried on 

 during the past 25 years in Florida, the Bermudas, Bahamas, Cuba, 

 Jamaica, and the West Indies in the Atlantic. They include in the 

 Pacific the Galapagos, the Hawaiian Islands, the Great Barrier Reef of 

 Australia, the Fiji Islands, and the Coral Reefs and Islands of the 

 tropical Pacific, from the i Marquesas to the Paumotus, the Society 

 Islands, the Cook Archipelago, Niue, the Tonga, Ellice, Gilbert, and 

 Marshall Islands, the Carolines and Southern Ladrones, and the 

 Maldives, in the Indian Ocean. 



Recognising that Darwin's theory did not explain the conditions 

 observed, my reports were limited to descriptions of the different types 

 of Coral reefs and of the causes to which they probably owed their 

 formation, and no attempt was made to establish any independent 

 general theory. 



Beginning with the Barrier Reefs, we find that those of Fiji, the 

 Hawaiian Islands, and the West Indies usually flank volcanic islands 

 and are underlaid by volcanic rocks. Those of New Caledonia, 



