302 proceedings: geological society 



drainage basins l)y glacial obstruction: the establishment of drainage 

 lines across the lowest available divides; and the topographic adjustment 

 of the present river systems. The maximum known extent of ice in 

 late geologic time is inadequate to the requirements of this hypothesis, 

 but data bearing on this point are incomplete. 



Igneous rocks of the Raton Mesa Region: J. B. Mertie, Jr. The 

 mesas near Raton, New Mexico, have resulted from the differential 

 effect of erosion upon a series of lava flows and the surrounding sedi- 

 mentary rocks. The vulcanism began in post-Eocene time and con- 

 tinued intermittently to recent time. The oldest flows cap the highest 

 mesas, thus preserving the original land surface over which they spread; 

 while the latest flows lie in the present lowlands. Four series of flows 

 have been recognized on the basis of erosional unconformities which 

 separate them. The first or oldest series is composed of numerous 

 fissure flows of great thickness and originally of great extent. They 

 are uniformlj^ olivine basalts. The second series is not materially dif- 

 ferent from the first. The third series contains a variety of rock types, 

 among which hornblende hyalorhyolite, cegerite trach}^e, augite ande- 

 site, hauyne basalt, basanite, quartz basalt, and normal olivine basalt 

 have been recognized. Many of these flows came from central vents, 

 and most of the resulting rock types show greater or less amounts of 

 glass. The flows of the fourth series have come in every instance from 

 volcanic cones of the central type and are uniformly glassy in character. 

 They are, so far as observed, normal olivine basalts. The dyke rocks 

 of the area include kersaijtites, vogesites, camptonites, limburgites, and 

 nephelinites. 



The results of the investigation show a gradual change from the 

 fissure to the central type of eruption, an increasing viscosity in the 

 lavas accompanied by explosive volcanic action, and the development 

 of numerous extreme rock types, or magmatic end products. All these 

 phenomena are interpreted as the results of dying volcanic activity. 



Remarks on the geology of the Bahama Islands, and on the formation of 

 the Floridian and Bahaman oolites: Thomas Wayland Vaughan. The 

 author gave a brief resume of some studies he has conducted during the 

 past seven years under the joint auspices of the United States Geological 

 Survey and the Department of Marine Biology of the Carnegie Insti- 

 tution of Washington. The remarks on the geology of the Bahamas 

 were based on observations made and material collected by him as a 

 member of an expedition conducted by Dr. A. G. Mayer of the latter 

 organization, during last April and May. 



The submarine and subaerial topographic features of the Bahamas 

 were described briefly. The general country rock, across the Great 

 Bahama Bank from Gun Cay to Northwest Passage and that of New 

 Province and Andros islands, is oolite similar to the oolite of Florida. 

 Along the windward faces of the islands ridges of wind-blown material 

 rising above the lower platforms are usual. 



The studies of Dall, Sanford, and the author, in association with 

 Geo. C. Matson, led to the opinion that the finely divided calcium car- 



