THE STKATIFIED ROCKS OF ESSEX COUNTY. 
BY JOHN H. SEARS. 
The term "stratified rock" is applied to different rock 
formations in wliich stratification is the only common char- 
acter, and although the syenites, diorite, felsites and some 
of the so-called breccias show stratification in part, there is 
little difficulty in separating them from the groups con- 
sisting chiefly of limestones, quartzites and argillaceous 
rocks of which this paper treats. 
Nearly one-half of the bed rock of Essex County is dis- 
tinctly stratified, and by means of our knowledge of these 
groups the geologic age of all the other rock masses may 
be approximated. • 
When we consider the frequent faulting of the rock 
formations and the great area which is covered by drift 
sand, gravel, clay and till, leaving only occasional outcrops 
for examination, the difficulty of preparing a correct map 
of the underlying rocks of the county may readily be seen. 
The stratified rocks of the county which are here to be 
considered are divided into several groups. The principal 
ones are the limestones, argillites, quartzites, and shales 
of detrital origin, and the schists, amphibole and granitic 
gneisses of doubtful derivation ; the whole to be classed 
as more or less metamorphic, a condition clearly revealed 
by the microscope when these rocks are studied in thin 
section. The eflfects of metamorphism on rocks are con- 
solidation, loss of material by chemical solvents, change of 
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