104 
dorite from Etna, a mean of 2°625. An analysis given by 
Prof. Cook, (Geol. of N. J., p. 215) of rock from the same 
region, corresponds with this conclusion : 
Calculated Calculated 
ErieTunnel Rock.) Labrador,66. | Labrador,60. 
Geo, H. Cook. | Hypersthene,33. | Hypersthene,40. | H. Wurtz. 
fDensities. | 2°94 | 2°93 ] 2°98 | 2-983 
Silica, 53-9 53-4 535 eel 
Alumina, Lita) 20-2 18:2 
Magnesia, 10°3 8:2 8:7 
Lime, 8:0 8-0 v4 
Ferrous Oxide, 8-0 7:2 8:7 
_ Soda and Potash, 2'3 30 27 
The Feldspar cannot be either Orthoclase or Oligoclase, 
because there is too little Potash and Soda respectively, nor 
Albite nor Andesite, because too little Silica. Prof. Cook 
gives many other analyses of traps from other parts of New 
Jersey, generally, nearly corresponding to this. A trap from 
Haverstraw, at the northern end of the Palisades, gave Prof. 
W. density 2:92. 
Many density determinations have also been made of 
samples of the so-called Sandstones and Shales, preparatory 
to analyses thereof: All these were taken «pon small 
fragments, by the method with a stoppered bottle. One from 
Haverstraw Quarries, (underlying the above trap,) gave 
2°608; one from Newark, 2589; and soon. These results 
being lower than expected, led to careful examinations of the 
materials making up these so-called Sandstones, and with 
some surprise it was found that the angular granules 
were almost entirely Feldspar, nearly and in some cases, 
quite free from Crystalline quartz. It is supposed that in 
analyses of these rocks, (the varieties in use for building 
purposes are referred to,) the portion insoluble in Muriatic 
Acid has heretofore been assumed to be Sand, without 
further examination, and that this fact has thus escaped 
notice. As before stated, these Feldspathic fragments are 
chiefly concreted by soluble Silica. Density determinations 
of the ‘Shaly ” beds gave much higher figures, mean about 
2°84. This is much too high for any Kaolinite, of which 
