532 C1, LIEN 
hornblendic and micaceous gneisses, and the presence of magnetic 
iron ore, suggest a detrital origin for at least a part of the gneisses, 
and consequently their reference to the Algonkian. There may be 
really two series of rocks: (1) A series of limestone and associated 
interbedded rocks, of sedimentary origin, and (2) a series of more 
massive granitoid gneisses, probably older, and of unknown origin. 
This supposition is based only on the fact that the limestones are 
persistently associated with the hornblendic and micaceous gneisses and 
quartz-pyroxene rock, and are not found associated or in contact with 
the light colored granitoid gneisses which constitute the main mass of 
the mountain. However, there is not sufficient evidence to refer a 
a part of the gneisses to the Algonkian, and all are therefore classed 
as pre-Cambrian. 
The crystalline limestones are believed to be distinct from and 
older than the blue magnesian limestone of Cambrian age, which 
occurs along the northwestern side of the New Jersey Highlands, and 
and which outcrops in isolated areas in the valleys adjacent to Jenny 
Jump Mountain, 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, showing that they have been subjected to 
genera] metamorphic forces of which the neighboring blue limestone ° 
shows no trace. 
2. They occur in intimate association with the gneisses, which are 
of admitted pre-Cambrian age. 
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 not due to the action 
of eruptives by which they are cut; so that no sufficient agent 1s at 
hand to account for the supposed change from blue into white lime- 
stone. The white crystalline limestones are therefore believed to be 
of pre-Cambrian age. 
Williams and Clark’ describe and map the geology and physical 
features of Maryland. The pre-Cambrian rocks, described by Williams, 
‘Geology and physical features of Maryland, by G.H. WILLIAMS and Ws. B. 
CuaRK: Extract from World’s Fair Book on Maryland, Baltimore, 1893, pp. 1-67. 
With map. 
