6 +2 THE POPULAR SCIENCE MONTHLY. 



York Island has so great a similarity to some portions of the Lauren- 

 tian series in Canada that it is difficult to resist the conviction that they 

 are of the same age. 



The Canadian series is supposed to be not less than 50,000 feet in 

 thickness, consisting of somewhat different elements in different parts, 

 but mainly of gneiss and crystalline schists with numerous beds of dolo- 

 mitic marble and serpentine, and containing, as most characteristic 

 minerals, magnetic iron-ore and apatite (phosphate of lime). The beds 

 stand at a high angle, and, although having once formed great folds and 

 even mountains, by ages of surface-erosion they have been worn down 

 to a merely undulating surface. On the east bank of the Hudson, at 

 and above New York, we have almost precisely the same state of things, 

 viz. : 1. A belt of crystalline rocks forming apparently a continuous 

 series to and beyond the Connecticut line ; 2. Strata set nearly vertical, 

 once forming high hills or mountains, now worn down by long exposure 

 to a mere rolling surface ; 3. The series composed chiefly of gneiss and 

 crystalline schists, with heavy beds of dolomitic marble and thinner 

 bands of serpentine ; and, 4. Containing in its western portion where 

 it joins the New Jersey iron belt with which it is inseparably connect- 

 ed important beds of magnetic iron-ore, while apatite is one of the 

 most common disseminated minerals. From these and other reasons 

 which might be mentioned, the New York rocks are regarded by the 

 writer as of Laurentian age. They seem to have formed a ridge which 

 was a part of a range of highlands that ran down on the eastern side 

 of our continent, having the same general direction with the Allegha- 

 nies, but being very much older than the more recent folds of that 

 chain. Indeed, judging from the character of the rocks composing it, 

 the immense amount of surface-erosion it has suffered, and the absence 

 of overlying strata, we must regard it as one of the oldest portions of 

 the continent. 



Staten Island is in part a continuation of the New York belt of 

 Laurentian rocks the eastern side being composed of granite and ser- 

 pentine, the western of trap and Triassic sandstone and owes its relief 

 to that fact. South of this point the ridge sinks down and is covered 



* 



Hudson River Laurentian? Belt Trias Conn. R, 



Profile Section from the Hudsdn to the Connecticut.. 



Fig. 1. 



with more recent strata, but it apparently reappears at Trenton and 

 Philadelphia. Thus it would seem to be a sort of spur of the Blue 

 Ridge, the oldest chain of the Alleghany belt, diverging from it in 

 Fulton County, New York, and following a nearly parallel course south- 

 westward. 



