1889. | NEW YORK ACADEMY OF SCIENCES, 55 
and 90th streets, and west of Eighth avenue, the angle of the 
outcropping rocks may be as high as 80° and over. 
Rock Scheme. In the Gneiss Belt the layers succeed as 
. follows: 
1. Muscovite gneiss (bottom rock); 2. Mica schists and bio- 
tite gneiss: 3. Amphibolites and pyroxenites; 4. Pegmatite and 
granite. 
Geological Age. Though lithological study in itself is not 
sufficient to establish the definite age of a rock, the occurrence 
of gabbro and of the granulites, taken in connection with the 
entire absence of any fossils, etc., may justify the conclusion 
that our island belongs to the upper series of the Archean age. 
The quaternary age is represented by moraines, clays, gravel- 
beds, and in some locations by a soft mica schist, mixed with 
kaolin, which hardens on exposure, and which unquestionably 
consists of the rock-meal or detritus, ground down by glacial 
action. These ancient lake-bottoms are filled in with bowlders 
and detritus. 
Pror. MARTIN stated that the suggestion had been recently 
made by Cart. A. W. Voapes that great advantage might be 
derived from the passage of a city ordinance requiring that 
wherever excavations are made by the city, or permits given 
therefor to individuals or contractors, it should be required that 
typical specimens of the rock be secured and deposited in some 
assigned and permanent place, such as the City Hall, the Amer- 
ican Museum, or the College of the City of New York. In this 
way the distribution of rocks throughout at least the upper part 
of the island might be made a matter of permanent record. He 
suggested that the Academy should take some action for carry- 
ing out this idea of Capr. VOGDEs. 
Ex-ALDERMAN CONKLING said that he had no doubt that if 
such an ordinance were proposed, and the reasons for it laid 
before the Board of Aldermen, there would be no difficulty at all 
in regard to its adoption. 
The suggestion was discussed by several members; and it was 
voted to appoint a committee to take steps toward securing such 
an ordinance, the committee to report to the Academy before 
taking positive action. 
Messrs. D. S. Martin, Gro. F. Kunz and W. H. J. SIE- 
BERG were named as the committee. 
