328 ANNALS NEW YORK ACADEMY OF SCIENCES 



Twenty-two persons were present. 



The minutes of the last meeting of the Section were read and approved. 



The following program was then offered: 



Robert T. Hill, The Geology of the Sierra Almaloya, Mexico. 

 Alexis A. Julien, Evidence or the Stability of the Rock Foundations 

 OF New York City. 



Summary of Papers. 



Professor Hill gave a discussion of the tectonic structure of the northern 

 part of the Mexican Plateau introduced by a detailed description, with 

 topographic maps and lantern illustrations, of the geology of the Sierra 

 Almoloya, a small mountain of Comanche Cretaceous limestone, situated 

 between Jimenez and Parral, in the southern part of the State of Chihuahua, 

 Mexico. 



He described the Mexican Plateau as having stood several thousand feet 

 nearer sea level at some late geologic epoch, and stated that it, together with 

 the Colorado Plateau, and probably the whole Rocky INIountain region, had 

 participated in a great epeirogenic uplift, as measured by the similarity of 

 depth of the canyons of the Colorado, the Rio Grande, the Rio Lerma and 

 the Balsas. The summit of the plateau of Western Sierra Madre in Chihau- 

 hua, and other tops, save the more modem constructional volcanic piles, 

 were described as remnants of the older peneplain before its uplift. 



The mountains of Chihuahua, east of the Western Sierra, were described 

 as necks and stubs representing the survival of the hardest in the degrada- 

 tion and lowering by desert denudation of the old plateau level which once 

 occupied it, and the stripping away of two thousand feet or more of ejecta 

 dowTi to the once buried limestone basement. 



The structure of the Almoloya moimtain was shown to consist of most 

 complicated recumbent folds, thrown over from the west, and of the Alpine 

 type. The mountain was also of interest inasmuch as its structural axis 

 was in a northeast direction. 



Professor Hill's paper was discussed by Professor J. F. Kemp, Dr. E. O. 

 Hovey and others. 



Dr. Julien then spoke on the "Evidence of the Stability of the Rock 

 Foundations of New York City." The general facts were reviewed which 

 might justify the confidence of builders in the operations of extensive con- 

 struction 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 shat- 



