868 



SCIENCE 



[N. S. Vol. XXV. No. 648 



THE NEW YORK ACADEMY OP SCIENCES 



At the meeting of the Section of Geology 

 and Mineralogy, January 7, the following 

 paper was presented: 



Volcanoes of CoUma, Toluca and Popocate- 

 petl: Edmund Otis Hovey. 

 Toluca is the oldest of the three volcanoes. 

 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, with regard to origin. 

 The volcano of Popocatepetl shows its com- 

 posite character as a strato-volcano in the 

 walls of the crater, and streams of lava have 

 been among the features of the most recent 

 eruptions. The volcano of Colima is still 

 sending up a vigorous column of steam from 

 its central summit crater. From this summit 

 crater there poured out, in the latest eruption 

 (1903), streams of very frothy lava which 

 present a strange appearance on account of 

 the porous character of the surface blocks. 

 The same feature characterizes the streams of 

 the earlier eruptions and has led some observ- 

 ers to the erroneous conclusion that flows of 

 lava have not occurred at the volcano of 

 Colima. 



The major portion of the evening was then 

 devoted to an examination of the exhibits of 

 geology, paleontology and mineralogy in the 

 New York Academy of Sciences Exhibition, 

 under the guidance of the committeemen in 

 charge of those exhibits. 



At the meeting, April 1, Mr. Robert T. Hill 

 gave a discussion of the tectonic structure of 

 the northern part of the Mexican Plateau, 

 which was published in Science for May 3. 



Dr. Alexis A. Julien then spoke on the 

 ' Evidence of the Stability of the Eock 

 Eoundations of New York City.' The general 

 facts were reviewed which might justify the 

 confidence of builders in the operations of 

 extensive construction now in progress. Two 

 former periods of enormous seismic activity 

 in this region were considered, as recorded by 

 the violent faulting produced at each time. 

 The one, connected with the foldings, slips and 

 shattering during the great Appalachian up- 



lift, and now revealed by the numerous peg- 

 matite intrusions cutting irregularly across 

 the stratum of crystalline schists, probably 

 effected during Cambrian time. The other, 

 after the close of the Mesozoic, during the 

 thrust of lava sheets between the sandstones 

 and shales of the Newark series of New Jersey, 

 now indicated by many faults across Man- 

 hattan Island and the adjacent Palisade 

 Ridge. The long period of cessation of uplift, 

 of ensuing subsidence and extensive surface 

 erosion, offers the conditions in this region 

 which promise long stability, notwithstanding 

 the slight tremors noted at intervals of thirty 

 or forty years. In the absence of disturbance 

 of the glacial striae, everywhere abundant, 

 which serve as natural benchmarks to record 

 changes of level or faulting, we obtain there- 

 fore direct testimony to the established ab- 

 sence of tremor during the long and approxi- 

 mately definite period which has elapsed since 

 the passage and withdrawal of the continental 

 glacier. In other parts of the Hudson River 

 valley, however, some evidences of post-glacial 

 faulting have been observed. 



Alexis A. Julien, 

 Secretary of Section 



THE ELISHA MITCHELL SCIENTIFIC SOCIETY OF 

 THE UNIVERSITY OP NORTH CAROLINA 



The 172d meeting was held in the main 

 lecture room of Chemistry Hall, Tuesday, 

 April 16, 7:30 p.m., with the following pro- 

 gram: 



Peofessob Abchibaid Hendebson: 'The Foun- 

 dations of Geometry.' 



Pkofessoe Chas. H. Hebtt : ' The Optical Rota- 

 tion of Turpentines.' 



Alvin S. Wheeler, 

 Recording Secretary 



DISCUSSION AND CORRESPONDENCE 

 the clocks of the GREENWICH AND U. S. 



naval observatories 



To THE Editor op Science: In Professor 

 Eichelberger's paper, published in your issue 

 of March 22, 1907, he gives a comparison 

 of the performance of six clocks, at various 

 periods from the time of Bradley in 1750. 



This table is primarily intended to show the 



