214 TRANSACTIONS OF THE [May 21, 
Grains of pyrite are not uncommon, but are quite irregularly 
distributed and of no great importance in the rock. 
The total amount of diabase contained in these dikes is suf 
ficient to render it a not unimportant factor in the geology of 
the region. If the number of dikes be placed at thirty, and the 
average thickness be taken as ten feet, both of which quantities 
are doubtless below the actual amount, it is evident that there is 
present the equivalent of a sheet of diabase three hundred feet 
thick. Such a thickness would be important in a bedded series, 
and is of no less moment in the present instance. The element 
of extension along the strike of the dikes is lacking, but the 
indications in the field point to a measure of several miles. 
The uniformity in the strike cannot be accounted for by in- 
trusion along bedding planes, as most of the dikes are in massive 
granite. It suggests that the diabase was injected into fissures 
produced by a general and uniform disturbance, while the ab- 
sence of any considerable dynamo-metamorphism in the dikes 
demonstrates that during the great length of time that has 
elapsed since the intrusion the region has been nearly free from 
the action of mountain-making forces. 
From its coarseness of grain it is safe to conclude that the 
diabase solidified at considerable depth, though not so profound 
as to prevent the granite from being cool and chilling the dia- 
base along the contact, Whether or not the dikes are conduits 
that once led up to surface flows, it is impossible to say, all 
trace of such flows, if any ever existed, having been removed by 
denudation. 
HAMILTON COLLEGE, CLINTON, N. Y., April, 1894. 
THE GEOLOGY OF ESSEX AND WILLSBORO’ 
TOWNSHIPS, ESSEX CO., N. Y. 
By Tueopore GREELY WuitE, Pu. b. 
(Puates VI. & VII.) 
CONTENTS. 
Introduction and General Features: Formations represented; Archean 
Norites, Limestone, Schists and Granites; Cambrian: Potsdam Quartzite; 
Ordovician : Calciferous Sandrock, Chazy Limestone, Trenton Shaly 
Limestone, Utica Shale; Quaternary : Champlain Clays, Delta Deposits 
and Drift; The Dikes; Appendix I: Record of Dikes; Appendix II : 
List of Fossils collected. 
