272 ROYAL SOCIETY OF CANADA 



where the spaces are relatively larger, doubtful hyclronephelite and a car- 

 bonate are found to have crystallized out. Where the fine grained ma- 

 terial is found without the hydronephelite, the carbonate generally lines 

 the cavity ; in other instances the carbonate fills the interior, with a hydro- 

 nephelite rim. 



Two features presented by this contact are to be particularly noted, 

 namely the brecciation and the alteration. Of the various formations 

 present in the district, the Utica shale is by far the most friable. This 

 fact that the Utica lends itself so readily to brecciation, suggests a con- 

 nection with the fact that this, which is by far the largest of the occur- 

 rences, is found in the Utica. Further, the alteration of the shale to horn- 

 stone indicates that there was considerable heat attending the advent of' 

 the breccia. In brief, therefore, the brecciation indicates dynamic action, 

 and the alteration heat, thus suggesting an igneous intrusive, and so 

 confirming the conclusions arrived at from the petrography alone. 



Besides the ordinary inclusions, the breccia holds three large 

 masses of limestone, which merit special mention. These occur on the 

 northeast side of the island. The middle exposure is lenticular in shape, 

 and is cut by a dyke which has been subsequently faulted. It has an 

 area of about 100 square feet. The rock is a fiine grained, light grey 

 friable limestone. The north exposure is 200 feet in length, and is a dark 

 grey line grained semi-crystalline limestone which is somewhat bitu- 

 minous. It has been brecciated along the contact with the breccia, and 

 the angular fragments have been cemented by a paste which differs in 

 composition from the limestone. On a weathered surface this matrix 

 stands in relief forming a complicated network, which shows the most 

 minute detail in structure. Immediately south of these two there is an- 

 other large block of granular siliceous limestone also imbedded in the 

 breccia. These masses of limestone are all highly fossiliferous and have 

 been made the subject of a careful palseontological investigation by Dr. 

 H. S. Williams, the detailed results of which are given in a separate 

 paper. Briefly, he finds the first two masses to be of the same age, the 

 Helderbergian of the New York series. The block of siliceous limestone 

 is later and equivalent to the Oriskinian. 



An east and west section across the larger limestone inclusion and 

 the breccia shows the relations of the two, and from this it is apparent 

 that at an earlier period the former was wholly enclosed in the latter. 

 (See fig. 19.) 



Thin sections of the breccia showed fragments of hornstone, 

 sandstone and granite; also grains of quartz, zircon and felspar, in a 

 groundmass of apatite, perovskite, pyrite, hydronephelite, epidote, car- 

 bonates and doubtful melilite. The hornstone consists of minute grains 



