150 Study of the Neiv York OI)eHi<k as a Decayed Boulder. 



then carried on too rapidly to insure, in such spots, an infiltration 

 of melted paraffin to a sufficient depth for perfect safety. 



On June 30, 1890, the Park Commissioners appointed a Second 

 Committee, consisting of the late Prof. John S. Newberry, (Prof. 

 Albert H Gallatin, who was unable to serve) and the author, to 

 carry out the proposed experiment and define the details of the 

 modified process. On July 24, this Committee sent in their Re- 

 port. This and the preceding Report (with the exception of its 

 Appendix and chart) have been printed by the Park Department, 

 but only in small number. It is therefore desirable to present here 

 the principal facts, including the more scientific and technical details. 



"The object of the experiment was to determine the best condi- 

 tions for the re-treatment of the decayed spots upon the Obelisk 

 during the coming month of August. ... It was necessary in the 

 first place to obtain a large block of granite of approximately the 

 same mineral composition and texture as that of the Obelisk, and, if 

 possible, of the same size." After much exploration of the granite 

 yards of New York City to obtain the use of a block of sufficient 

 size, and many inquiries concerning the granite quarries up the 

 Hudson River, in Connecticut, near Saybrook and along the Sound, 

 and in the islands off the coast of Maine, " our attention was directed 

 to the many large transported boulders of granite or coarse granitoid 

 gneiss which are strewn over the surface of Westchester County. 

 In masses of rock like these, exposed to the weather for ages, we 

 might fairly expect to find the better material for which we were 

 looking — that which had experienced an incipient internal decompo- 

 sition and increased, power of absorption, as in the granite of our 

 ancient Obelisk. Near Tuckahoe and New Rochelle several such 

 boulders were found, though of insufficient size, on the lands of 

 Mr. F. Wiede and of Mr. C. Morgan, to whom also our thanks are 

 due for offered assistance. 



At last, near the summit of a hill on Midland Avenue, about two 

 and one-half miles southwest of Bronxville, an enormous boulder, 

 nearly twenty feet in height, of granitoid gneiss, was found on the 

 DeWitt property, which seemed well enough suited for our object. 

 Its mineral components were found to be very nearly the same as 

 those of the Obelisk, viz. : white feldspar (triclinic), potash feldspar, 

 quartz, hornblende, biotite-mica, and a little garnet, magnetite, etc. 

 The volume of the entire boulder was measured and ascertained to 

 be nearly three times that of the Obelisk j but it was divided in two 



