A NEW INTRUSIVE ROCK NEAR SYRACUSE. 477 



The last j^aper of the section was — 



A NEW INTRUSIVE ROCK NEAR SYRACUSE 

 BY N. II. DARTON AND J. F. KKMP 



[Abstract'] 



Contents Page 



GeoloKy (by N. H. Darton) 477 



Petrography (by J. F. Kemp) 477 



Geology (by N. II. Dauton) 



The dike "svas brouirlit to my attention l)y iSIr P. II. Schneider, of Syracuse, and 

 to liim I am also indebted for information regarding? some of the relations. The 

 locality is on the toj) of an isolated hill half a mile south of Dewitt Center (Desono 

 station), about three miles east of Syracuse. The dike was exposed by excavations 

 for the reservoir, and does not appear to have reached the natural surface. It was 

 buried under a mantle of glacial drift, and in part at least covered by shales and 

 limestones of the Salina formation. Unfortunately the reservoir was completed 

 and partially tilled with water before INIr Schneider learned of the dike, so that he 

 was unable to observe the relations. According to the statements of the contractor, 

 the rock occurred in masses imbedded in a greenish, yellow earth, which underlaid 

 the entire area of the excavation, about 200 by 250 feet. Some of the masses were 

 20 by 50 feet. 



The greenish yellow earth in which those masses occurred is undoubtedly a de- 

 composition product from the intrusive rock. The original surfixces of the masses 

 themselves are more or less deeply decomposed to a serpentinous matter, and some 

 of the smaller ones are thoroughly altered to secondary })roducts, which are filled 

 with calcite veins. Whether the mass is a dike or an intruded sheet was not de- 

 termined, but it is probaljly the former. No traces of the rock have been found in 

 wells or on the surface in the vicinity. 



The dike at Dewitt is in the upper portion of the Salina formation, which consists 

 of shales and limestones. A short distance south the slopes of the Ilelderberg 

 escarpment arise, and to the north are wide plains of the Salina beds. The dip is 

 that of a gentle monocline to the southward. The rocks adjoining the intnisive 

 dike pre.«ent signs of slight metamorphism, as indicated by increase in hardness and 

 darkening of color. Mr Schneider has called my attention to an exposure GOO yards 

 north of the reservoir in which there is considerable (lexing of the shales, but this 

 was the only sigu of disturbance noted. 



The intnision contains many inclusions of various rocks, wliii-h will Ijc referred 

 to by Profe.s-sor Kemp. The relations of the Dewitt dike to the similar occurrences 

 at Syracu.se are not known, but it is probable that they are connected underground. 

 A search should Ikj made for other dikes in the region. 



Petroguaimiy (by J. F. Kicmp) 



The dike is a peridotite very similar to the one earlier discovered at Syracuse, 

 but it is much fresher than anything collected there. It has large and abundant 

 pr>rphyritic crystals of olivine, which are perfectly unaltered, even the usual change 

 to s<'rpentine failini: in many. There are also a few i)henocrysts of monodinic 

 pyroxene, and considerable brown biotitc in hexagonal crystals. The original 



