138 ME. J. ROiiAXEs OX THE [Feb. 1912, 



possible. Finally, I take this opportunity of thanking Dr. J. E. 

 Marr, F.K.S., and Mr. E. H. Rastall for their kind help and 

 interest during the working-out of my material. 



EXPLANATION OF PLATES VIII & IX. 

 Plate VIII. 



Fig. 1. Concentric jointing in lava, El Brazil. (See p. 117.) 



2. Alluvium, Salinas Bay, near Puntarenas, showing the old sea-cliff in 

 the background. (See p. 132.) 



Plate IX. 

 (All figures are enlarged X 20 diameters.) 



Fig. 1. Sau Miguel Limestone, sliowing section of Balanus. (See p. 108.) 



2. ]\Ionzonite from the Cerro Caudelaria. (See p. 111.) 



3. Limburgite, near Manzanilla, showing olivine in process of replacement 



by serpentine; the numerous small granules are augite. (See p. 129.) 



4. Breccia with foraminifera, Manzanilla. (See p. 130.) 



DlSCTJSSIOX. 



Dr. J. E. Maer commented on the great difficulties vrith which 

 the Author had been confronted, owing to climate, growth of 

 vegetation, and other causes. He knew of these difficulties from 

 letters received when the Author was carrying on his work. 

 Prof. Suess had especially cited Costa Rica as a country where 

 further work was required, and the speaker believed that the 

 Author's extensive collection of new facts would be of great value 

 in adding to our knowledge of a little-known country. He knew 

 that the Author had done more work than was incorporated in the 

 paper, as, for instance, in the j)eninsula of ]^icoya, but that he 

 wished to return to the area before publishing his account of that 

 work. The speaker hoped that this further work would be prose- 

 cuted, and felt that the results of the journey which were that 

 night brought before the Society augured well for such future work. 



Prof. T. McK. Hughes pointed out that the Author had not had 

 time to make a survey of the district, and that the map he exhibited 

 had very well served the purpose of indicating the position of the 

 places mentioned in their relation to one another and to the sea on 

 either side. The Author had met with other unexpected difficulties, 

 besides those arising from the country which he was sent to 

 explore. He had very clearly laid before them the character of the 

 rocks exposed and the fossils and mineral constituents, so far as he 

 had in the limited time at his disposal been able to gather suflBcient 

 for the discrimination and identification of those rocks. He had 

 explained the apparent and inferred sequence, and had suggested a 

 geological history of the district. One of the most interesting 

 inferences arising out of this was that geographical changes had 

 taken place in comparatively recent ages, which involved a sub- 

 mergence of the isthmus and alternate separation and union of the 



