764 



SCIENCE 



[N. S. Vol. XXV. No. 646 



gations. In America Selwyn -wrought from 

 December, 1869, to January, 1895, a period 

 of twenty-five years. He traversed the 

 continent before the transcontinental lines 

 of railways were built and directed the 

 efforts of his staff to many of the portions 

 of Canada whose resources to-day prove of 

 such remarkable value. He received many 

 distinctions at home and abroad. 



Cave-Sandstone Deposits of the Southern 



Ozarks: A. H. Purdue. 



The rocks exposed within the area treated 

 of in this paper are of Ordovician, De- 

 vonian and Carboniferous ages. Near the 

 top of the Ordovician of the area is an 

 unconformity upon which the Upper St. 

 Peter sandstone is put down. Those por- 

 tions of the sandstone that are put down 

 in basins and cistern-like depressions are 

 frequently preserved from erosion and 

 stand up as conspicuous sandstone masses. 

 Below this horizon, and at different levels 

 in the Ordovician limestone, standing up 

 on the sides of the ravines, are numerous 

 large sandstone masses, similar to those 

 already mentioned. These sometimes occur 

 singly and sometimes collectively, one above 

 the other. For several reasons, which are 

 stated, these are considered to be cave de- 

 posits. The sandstone is of the same gen- 

 eral character as that constituting the St. 

 Peter, and is supposed to be of the same 

 age. The manner of introduction of the 

 sand and the age of the caverns was con- 

 sidered. 



Professor Purdue's paper was discussed 

 by Professors Grabau, Jaggar, Willis, H. 

 C. Hovey, Puller, Hopkins and Davis. 



Volcanoes of Colima, Toluca and Popo- 

 catepetl: Edmund Otis Hovey. 

 The principal object of presenting the 

 paper was to show the society some photo- 

 graphs of these three volcanoes which were 

 taken upon excursions made in connection 



with the meeting of the tenth International 

 Geological Congress in the City of Mexico, 

 in September, 1906. 



Toluca is the oldest of the three vol- 

 canoes. A feature of greatest interest in 

 the crater is the dome of vitreous andesite 

 which welled up in the crater as the latest 

 phase of the activity of the volcano and 

 shows a certain resemblance to the cone of 

 Mt. Pele. The volcano of Popocatepetl 

 shows its composite character as a strato- 

 volcano with great clearness in the walls 

 of the crater, and streams of lava have been 

 among the features of the most recent erup- 

 tions. The volcano of Colima is still send- 

 ing up a vigorous column of steam from its 

 central summit crater. From this summit 

 crater there poured out, in the latest erup- 

 tion (1903), streams of very frothy lava 

 which present a strange appearance on ac- 

 count of the porous character of the surface 

 blocks. The same feature characterizes 

 the streams of earlier eruptions and has led 

 some observers to the erroneous conclusion 

 that flows of lava have not occurred at the 

 volcano of Colima. 



Current Methods of Observing Volcanic 



Eruptions: T. A. Jaggar, Jr. 



Dana's 'Characteristics of Volcanoes,' 

 based on the Hawaiian Islands, and books 

 with a Vesuvian bias have given undue im- 

 portance to lava in volcanology. As a re- 

 sult, active volcanoes have recently been 

 interpreted almost invariably as being actu- 

 ated by a rising lava column as first cause 

 of their explosions. Such interpretation 

 may be correct, but the evidence needs 

 careful sifting in every case, with the al- 

 ternative possibility in view, namely: (1) 

 That tectonic causes precede magmatic phe- 

 nomena, (2) that release of superheated 

 steam may be the first cause, (3) that new 

 lava may be a secondary product, and may 

 not appear at all. 



