664 The American Naturalist, [August, 
GEOLOGY AND PALEONTOLOGY. 
The Limestones of the Jenny Jump Mountains, New 
Jersey.—Accompanying the report on the Archean Geology of New 
Jersey, by Mr. J. E. Wolff is a paper by Mr. L. G. Westgate on the 
Geology of Jenny Jump Mountain, chiefly interesting on account of 
the conclusions reached by the author concerning the crystalline lime- 
stones of that region. 
The area under consideration embraces the northern half of Jenny 
Jump mountain in Warren county, New Jersey. This mountains lies 
along the northwestern border of the highland area, and is a sort of 
outlier or peninsula reaching into the later Paleozoic rocks. The main 
ridge of the mountain consists of gneisses; the limestone occurs at its 
extreme northeastern end, with outcrops along the southeast border of 
the mountain. 
The author discusses in detail the position, lithology and relations to 
the crystalline limestones in other parts of New Jersey, and reviews 
the views of previous writers as to the age of the Sussex county lime- 
stone, whizh has generally been considered the type and representative 
of other localities. Mr. diab views are given in the following 
summary 
“The crystalline limestones of Warren county are believed to be dis- 
tinct from and older than the blue magnesian limestone of Cambrian 
age, which occurs along the northwestern side of the New Jersey High- 
lands. They are believed to be distinct, for the following reasons.” 
“1. They differ lithologically from the blue limestone in being 
thoroughly crystalline, and in containing large amounts of accessory 
metamorphic minerals.” 
“2. They are intimately associated with and apparently interbedded 
with the older gneisses; and gneisses occur also interbedded in the 
limestone.” 
“3. They show no intimate association in areal distribution with the 
blue limestone, nor any tendency to grade into it.” 
“4, The metamorphic changes to which the white limestones have 
been subjected are general in their nature, and are not due to the action 
of the eruptives by which they are cut; so that no sufficient agent is at 
hand to account for the supposed change from blue into white lime- 
stone.” 
