472 RECORDS. 



pendent on the character of the cement and adhesion of the 

 grains; rigidity and tension. The " quarry sap," Dr. JuHen be- 

 lieves, plays a more important role than has hitherto been rec- 

 ognized, as it probably carries much of the cement in solution 

 and deposits it only when the stone is exposed to the air. This 

 accounts for the hardening of the stones after being quarried. 

 A distinction should also be made between porosity due to 

 cavities between the grains and interstices in the individual min- 

 erals. The former is a source of weakness, the latter not, al- 

 though either may cause the rock to exhibit a high absorptive 

 capacity. All of these points, which have an important bearing 

 on the strength of building stones are best studied with the 

 microscope. The paper was illustrated by means of sections 

 thrown on the screen with a polarizing lantern. Discussion 

 was by Professor Kemp and Mrs. Dudley. 



The second paper of the evening was by J. D. Irving on 



CONTACT-METAMORPHISM OF THE PaLISADES DiABASE. 



Mr. Irving referred to the work done by Professor Osann and 

 Andrae some years ago and stated that his results agreed with 

 theirs, but recent railroad excavations at Shadyside had enabled 

 him to obtain additional facts. The Diabase flow becomes 

 denser, finer grained and porphyritic towards the contact, with a 

 decrease of Hypersthene. In addition to zones found by Osann, 

 Mr. Irving found : i. A normal hornfels zone rich in Spinel. 



2. A hornfels zone with brown basaltic hornblende layers. 



3. Hornfels with an undeterminable isotropic mineral resemb- 

 ling Leucite. 4. Hornfels with Andalusite, gradually chang- 

 ing to Arkose farther from the contact. The Diabase is to be 

 considered as an intruded mass and not a surface flow. The 

 paper was discussed by Professors Kemp, Dodge, Dr. Hovey 

 and Mr. White. 



Owing to the lateness of the hour the reading of the other 

 two papers on the programme was deferred until the next meet- 

 ing. 



Academy adjourned at 10:15. 



Heinrich Ries, 

 Secretary of Section. 



