30 G. H. Williams — Peridotites near Peekskill. N. T. 



diorite), as shown in the accompanying map; and exposes its 

 eastern side in a high wall which is intersected by several line 

 grained d}?kes. It continues southward through the ch^solitic 

 area and crosses the point in a deep cutting where the contorted 

 mica-schists, their intersecting dykes and their contact with the 

 peridotite, are all distinctly to be seen. In a small railroad filling 

 near King's Ferry on the north side of Stony Point, large 

 quantities of the peridotite have been thrown out of the adjoin- 

 ing cutting and here many varieties may be collected. 



The most remarkable among these varieties is a dark green, 

 at first sight apparently fine-grained rock, which, however, 

 when held in the proper light, exhibits glistening, bronze-col- 

 ored cleavage surfaces often measuring 3x4 inches. The re- 

 flection from these surfaces is, however, not altogether con- 

 tinuous, being interrupted by small rounded grains of a dull 

 green mineral whose nature cannot be determined with the 

 unaided eye but which the microscope shows to be olivine or 

 serpentine. 



This is precisely the structure possessed by the "Schillers- 

 path " or "Bastit" of the Harz Mountains, which Professor 

 Aug. Streng described as long ago as 1862.* It does not differ 

 essentially from that of a feldspar crystal in graphic-granite 

 whose cleavage surface is seen in reflected light to be inter- 

 rupted by particles of uneven quartz. In fact this structure is 

 so common in many massive rocks, especially in the more basic 

 kinds, that I would venture to suggest the use of the term 

 " poicilitic " (derived from the Greek norAXoz, mottled) for 'it. 



Professor Pumpelly has described the same phenomenon in 

 the melaphyres of the Lake Superior region under the name of 

 '• luster-moltlings,'\ a term adopted by Professor Irving for a 

 similar structure which he found developed on a much larger 



the village of Schriesheim, a short distance north of Heidelberg in Baden, which 

 has been elaborately described by Prof. E. Cohen (Benecke and Cohen : Geog- 

 nostische Beschreibung der Umgegend von Heidelberg, 1881, pp. 141-148). This 

 investigator regarded the large bronzy-looking crystals, enclosing smaller grains 

 of the other constituents, as diallage. The same mineral is called " Schiller- 

 spath " by Fuchs and Bastite by G-roth. Very recently however Cohen has re- 

 vised his former determination and finds this mineral — as is the case in the 

 Cortlandt rocks — to be hornblende. He therefore proposes to call this type of 

 homblende-olivine rocks '' Hudsonite," on account of their extensive development 

 on the Hudson River. (Neues Jahrbuch fur Min., etc., 1885, II, p. 242.) This 

 name has already been used by Beck (Mineralogy of New York, 1842) for a vari- 

 ety of diallage occurring near Cornwall, N. Y., so that it would seem to the 

 writer preferable, if a new name is necessary, to adopt the term " Corilandtite " 

 for this class of rocks which play such an important role in the " Cortlandt 

 Series/' 



*He says: " Charakteristish fur den Schillerspath ist es, dass er uberall von 

 Grundmasse durchsetzt wird, so dass sein deutlichster Blatter-Durchgang mir 

 dunkeln, matten Fleckchen gesprenkelt ist." (Neues Jahrbuch liir Min., Geo! 

 und Pal., 1862, p. 533). 



f Metasomatic development of the copper-bearing rocks of Lake Superior. 

 Proc. Amer. Acad., vol. xiii, p. 260, 1878. 



