40 ARTESIAN WELLS ON THE ATLANTIC COAST. [bull. 138. 
There are also several superficial formations — the Lafayette, Colum- 
bia, and Trentou — consisting of sands, loams, and gravels, which 
thinly cover the lower lands and occupy certain higher regions. 
CHARACTERISTICS OF THE FORMATIONS. 1 
RARITAN FORMATION. 
This formation consists mainly of beds of clay and sand and admix- 
tures of these materials lying on the floor of crystalline rocks. As the 
slope of this floor is quite steep, the deposits thicken rapidly to the east 
and southeast and a thickness of 500 feet is soon attained. The basal 
beds often are coarse sands and gravels or bowlders, and these coarse 
materials always contain an abundant water supply. In some areas 
finer sands and even clays extend down to the crystalline floor. Local 
beds of coarse sand and gravel occur interbedded among the finer 
sands and clays in some areas, but their distribution is not fully deter- 
mined. The clays are of various colors, but red, gray, white, and buff 
are those most frequently observed. Ordinarily, they are in widely 
extended sheets, but they thin or thicken or merge into sands in a very 
irregular manner. Sands predominate in the upper portion of the for- 
mation. The basal beds outcrop along the Delaware River below Tren- 
ton, and in greater part extend to the Pennsylvania shore. From a 
few miles north of Trenton to beyond New Brunswick the formation 
lies on the eastern edge of the red sandstones and shales of the Newark 
formation. 
MATAWAN FORMATION. 
The deposits of this formation consist of dark-colored clays with 
intercalated beds and streaks of sand. The upper beds are predomi- 
nantly sandy. The mineral glauconite, or greensand, occurs in the for- 
mation to a small extent, mainly mixed with gray sand. Fossil shells 
occur in some of the beds at certain localities. Dr. Clark has esti- 
mated that the formation has a thickness of about 275 feet at its out- 
crop, but it appears to thicken rapidly to the eastward to over 800 feet 
in the deepest well at Asbury Park. 
In the outcrops in Middlesex and Mercer counties there appears to 
be no sharp break between the Matawan and the Raritan formations, 
but to the east and south the well borings have brought to light an 
intervening gravel bed which is an important source of underground 
water. In Maryland and Delaware the unconformity between the two 
formations is strongly marked, and the occurrence of this gravel bed 
appears to indicate the northern extension of this relation. 
NAVESINK FORMATION. 
This name has been applied to the Lower Marl bed, which is the next 
formation above the Matawan deposits and appears to merge into 
them. In its unweathered condition it consists of a greensand marl 
J The data under this subheading are largely derived from the reports by Prof. 
W. B. Clark, in the report of the Geological Survey of New Jersey for 1893. 
