FORMER HYDROGRAPHY OF MANHATTAN ISLAND 18 J 



As to the origin of the channels of Spuyten Duyvil creek and of the 

 Harlem and East rivers, in the opinion of the writer their directions have 

 been largely determined by lines of jointing and displacement. Regard- 

 ing the Spuyten Duyvil stretch, however, the facts are meager, and the 

 problem is not free from doubtful indications. 



Former Hydrography of Manhattan Island 



Owing to the early importance of Manhattan island and to the fact 

 that the gridiron of streets and avenues was laid out by surveys before 

 any considerable change in topography had been wrought by man, we 

 are in possession of unusually high-grade maps for the period in which 

 they were made. Randall's map of the island was published in sections 

 between the years 1811 and 1891. This map, which is now preserved in 

 the office of the commissioner of public works, comprises four volumes 

 of 92 sheets each. The individual maps are 25 by 37 inches, and are on 

 a scale of 100 feet to the inch. Randall gives the precise location of all 

 the old farms in their relation to water-courses and topography. General 

 Viele's map, published in 1874,* is on a scale of 1,000 feet to the inch, 

 and is based on Randall's map. It shows the original shoreline of the 

 island, the made land, the drainage system, the topography, and the 

 location of each rock exposure south of Manhattanville, all superim- 

 posed on the gridiron of streets and avenues. The accuracy of this 

 map has been abundantly attested by engineers, real-estate men, and 

 others who habitually use it, and, so far as exposures of rocks are con- 

 cerned, it has been attested by the writer, both by comparison with the 

 early reports of geologists on Manhattan island and by examination in 

 the field. The made land and the hydrography have been reproduced 

 in plate 35. It will be noted in how large a degree there is accord between 

 the drainage directions and the directions of streets and avenues. 



As an indication that this orientation of the drainage has been to a 

 large extent determined by planes of fracture, it is interesting to consult 

 the recent map by Julien, showing the location and orientation of the 

 principal dikes on the island. These dikes quite generally run along 

 the avenues (see plate 35). Julien has shown also that cross-fracturing 

 is a common feature of the rocks of the Manhattan uplands, and has 

 given instances of definite cross-faults directed nearly at right angles to 

 the avenues or along the cross-streets. Thus the fissure planes which 

 become occupied by the dikes and the perpendicular series described by 

 Julien (often occupied by quartz lenses and pegmatite) correspond very 

 closely in direction with the two series making up the main drainage 



* Topographical atlas of the city of New York, by Egbert L. Viele. 



