238 [ Assemble? 
Direction of Dykes ^ Veins ^ fyc. 
From a careful examination of the course and bearing of dykes, I have 
been disposed to adopt the opiniosn that they were produced by a cause 
acting uniformly, and in certain directions during a given period. The 
grounds on which an opinion of this kind is supported, may be gathered 
from the following facts: Dykes occur throughout the whole northern 
region, but there are a few localities at which they are numerous, and 
may be compared readily with each other. Of localities of this kind I 
will select Trembleau point in Essex county. In the immediate vi- 
cinity of this point, and within the distance of a mile, I discovered six- 
teen dykes. They vary in width from 2 or 3 inches to 10 feet. The 
average bearing is north 60° east. There are instances in which the 
bearing is north 80° east, and others in which it is north 40° east. 
Their direction is never in the line of the bearing of the strata or moun- 
tains, and wherever they belong to the primary rocks, I have never 
found their bearing due east and west. Though their bearing is not pre- 
cise'ly directed to a given quarter of the horizon, still, there is a great de- 
gree of regularity within certain limits. Hence the inference, that they 
may have produced by some cause, acting in a given direction during a 
single period. A few cases of single dykes may be referred to- for 
instance, one two miles south from the line of Willsborough, its bearing 
is north 70° east; another in Warrensburgh, north 45° east; another at 
the foot of the mountainous ridge between Glen's falls and Jessup's 
landing, north 70° east; another in Johnsburgh, near Mr. Rosevelt's, 
north 55° east. That portion of the dyke in contact with the adjacent 
rock is converte<l into obsidian. The few facts I have now given, 
though not sufficient to establish a general law, are still sufficiently re- 
markable to merit the attention of geologists in other sections of the 
country. 
List of Simple Minerals in the Counties of Essex and Warren. 
Limonite, eupyrchroite, magnetic oxide of iron, red oxide of tita- 
nium, brown tourmaline, schorl, zircon, yenite, chiltonite, obsidian, 
adularia, porcelain clay, hypersthene, labradorite, chalcedony, horn- 
blende, asbestus, serpentine, calcareous spar, apatite, pyroxene in all its 
varieties, garnet, colophonite, spinelle, sphene, graphite, sulphuret of cop- ^ 
per, sulphuret of iron, black oxide of manganese, silicate of manganese, 
lignite, steatite, talc, mica, crystallized quartz, scapolite, tabular spar, 
sulphate of magnesia. 
