14 ANNALS NEW YORK ACADEMY OF SCIENCES. 



aboard about 54 miles (by the river route) north of this, or possibly a few 

 miles north of Peekskill. 



W. W. Mather, 4 in 1843, described the rocks not as a series but merely 

 under the lithologic types of Westchester and Putnam Counties. Under 

 the caption "Sienite," he states that this rock forms the east bank of the 

 Hudson River below Peekskill and is found in many of the hills southeast 

 of Peekskill. It is valuable and a durable building stone, although rather 

 hard to dress. It changes east of Verplanck to a black hornblende rock, 

 which may contain iron. Pits have been sunk for coal in this rock but of 

 course without success. Under "hornblende rocks," he merely mentions 

 the dikes and stringers in the limestone at Verplanck. He evidently con- 

 siders the rocks adventitious occurrences of a syenitic type, making no 

 mention of the hypersthene, olivine, etc. and no suggestions as to their 

 origin. 



Herman Credner, 5 in 1865, made the earliest identification of the 

 hypersthene which exists in many of these rocks. After describing it 

 briefly, he states that there is a gradual transition of the hypersthene rock 

 into syenite and hornblende schist. His work, however, was hasty and 

 cursory and unsupplemented by the microscope ; and, since syenite is rare 

 in the district and hornblende schist unknown, his conclusions may be 

 disregarded. 



James D. Dana, in 1880, described these rocks in connection with his 

 work on the limestone belts of Westchester County, being the first geolo- 

 gist to recognize them as genetically related and to study them as a whole. 

 In his first paper, 6 he describes the rocks, classifying them as chrysolitic 

 and non-chrysolitic, and subdividing further into hornblendic, hypers- 

 thenic, augitic and biotitic rocks. He then discusses their origin. Since 

 they occur on Verplanck Point as dikes and stringers in the limestone and 

 schist, showing contact effects, he is led to believe that at one time they 

 had been molten, or at least plastic. From the considerable number of 

 schist and limestone inclusions in the western part of the district, which 

 generally lie approximately conformable to the strike of the main sur- 

 rounding areas of these rocks, he concludes that the Cortlandt Series is a 

 mass of old sediment, worked over by pressure and great heat ; these inclu- 

 sions would then be merely cases of unobliterated bedding. He finally 

 discusses the very sudden minor variations in the igneous rocks (which 

 are most frequent on Montrose Point) and believes that these also demand 



* Geology of New York, pt. I, Geology of the First District, p. 52S. 1S43. 

 6 "Geognostische Skizze der Umgegend von New York," Zeit. der deut. geol. Gesell- 

 schaft, XVII, 390. 1865. 



•Amer. Jour. Sci„ (3), XX, 194. 1880. 



