458 SCIENTIFIC RECORD FOR 1883. 



great bedded masses, the whole interstratified with the gneisses of the 

 series. 



He has further described the remarkable locality of serpentine on 

 Staten Island. This, which forms a bold ridge of some miles in length, 

 was formerly described as eruptive, and correlated with the intrusive 

 diabase belt of the Mesozoic, which extends parallel with it, a little to 

 the west, on the same island. While the Triassic sandstone lies along the 

 western base of the serpentine ridge, its southern and eastern bases are 

 covered by nearly horizontal Cretaceous beds. Britton, who redescribed 

 and mapped this region in 1880, regarded it as a protruding mass, belong- 

 ing to the Eozoic rocks below, a view confirmed by the present writer, 

 according to whom its prominent position is due to the fact that it was 

 left exposed by the subaerial decay of the inclosing gneiss rocks — which 

 became kaoliuized, while the serpentine, though softer, resists to a 

 greater extent chemical change — and was subsequently surrounded by 

 Mesoaoic strata, from the midst of which it now rises. 



The similar occurrences of serpentine in New York City, at Hoboken, 

 and again in Chester County, Pennsylvania, are also redescribed by the 

 Avriter. The latter appear as protruding masses among gneisses and 

 mica-schists referred to the younger or Montalban series; but it remains 

 uncertain whether their stratigraphical place is in these or in the older 

 Laurentian gneisses, which underlie them directly in these regions. The 

 Laurentian of the high lands on Manhattan Island appears to be 

 overlaid in parts by areas of younger gneisses and mica-schists, the 

 remaining portions of a mantle of Montalban ; a circumstance which 

 makes it doubtful whether the serpentine masses are to be referred to 

 the one or to the other series, though they are regarded as probably 

 Laurentian. 



The writer has also described in detail the mass of serpentine and 

 euphotide which rises from the Tertiary rocks at Monteferrato, in Tus- 

 cany, and shows that it is not intrusive, but a protruding portion of the 

 underlying Eozoic series, identical with the greenstone group of the 

 Alps, and probably Huroniau. He maintains the aqueous origin of ser- 

 pentine, and its formation from sea- water through the intervention of 

 solutions of silicate of lime or soda from subterranean sources. The 

 relations of the serpentine to the limestones, with which they are ofteu 

 associated, are compared to those of bedded or concretionary flint or 

 chert. While many geologists have concluded, from the results of micro- 

 scopic study and the frequent association of olivine and enstatite with 

 serpentine, that the latter has been formed by the hydration of the two 

 silicates before named, several recent Italian observers, among them 

 Issel, Mazzuob, and Capacci, suppose the material of serpentine to have 

 been ejected in a hydrated form from the earth's interior into the sea, 

 as an aqueous magma, which consolidated into serpentine, and by de- 

 hydration gave rise to the olivine and enstatite often found with it. 

 This hydroplutonic hypothesis, confessedly gratuitous, is a concession 



