372 The American Geologist. December, 1894 
are the most abundant rocks of the northwestern highlands, 
and in some cases the limestones appear to be interbedded 
with them. (4) The crystalline limestones at Oxford Furnace 
and Jenny Jump mountain in Warren county seem to be a 
southwestward extension of the Sussex county belt. An ex- 
amination of the geological map of New Jersey does not bring 
out this supposed relation with any marked distinctness. The 
Warren county rocks do not appear to be strictly a continua- 
tion of the northern belt, but to lie somewhat west of where 
the southern extension of the Sussex county rocks would 
naturally be expected. 
The crystalline limestones of the two areas have thus been 
classed together, because of their lithological similarity and 
their association with the gneisses, and not on good structural 
or paleontological grounds. Lithological resemblances among 
crystalline rocks are certainly insufficient proof of contempo- 
raneity. This is especially the case where the areas in ques- 
tion are at considerable distance from each other. In this 
case the nearest outcrops of the two areas are separated by a 
distence of sixteen miles. Where no contrary evidence occurs, 
however, lithological similarity has value as a suggestion; 
and when, as in the present instance, it is accompanied by 
association with a similar series of rocks — the granitoid 
gneisses — and the outcrops occur in a general way in line, it 
is very possible that the correlation between the two series of 
rocks which has been made in the past is correct. 
Views concerning the age of the crystalline limestones of 
New Jersey. Two different views have been held as to the 
age of the crystalline limestones of Sussex county and these 
views have been extended by their advocates to include the 
other crystalline limestones of the state. The view which has 
generally prevailed in the past, is that these limestones are of 
Areha?an age, and are members of the series of crystalline 
rocks to which the gneissic rocks of the highlands belong and 
with which the limestones are closely associated. The crys- 
talline structure and the abundant presence of accessory met- 
amorphic minerals, which are characteristics of these lime- 
stones, are considered due to the same general causes which 
have produced a crystalline structure in the gneisses with 
which they are associated. Among the geologists who have 
