CLAYS OF CRETACEOUS FORMATION, 153 



earth, containing gunpowder-like specks of black or dark-green 

 marl. This weathered phase is totally unlike the weathered 

 phase of 'any of the underlying beds, and it is thoroughly char- 

 acteristic of the Clay Marl series. The contact is usually a sharp 

 one, easily identified and readily located in the field, wherever 

 exposures are found from the Raritan river to Delaware bay. 1 

 The top of the Clay Marl series is likewise a definite line — the 

 abrupt passage from 1 a loose reddish sand often very coarse, with 

 grains of quartz the size of small peas to a compact greenish 

 marl. For much of the distance across the State the top of the 

 Clay Marl series is also marked by a fossil bed 1 to 4 feet in 

 thickness, which affords a definite and easily recognizable horizon. 



The outcrop of the Clay Marls extends from the shores of 

 Raritan bay across the State in a southwest direction to the Dela- 

 ware river north of Salem. It forms a belt varying in width 

 from 2^4 to 8 miles. Since the beds dip about 35 feet per mile 

 to the southeast, the belt of outcrop is widest where the slope 

 of the surface is toward the southeast, and narrowest where it 

 is steeply to the northwest. On Plate X the position of the two 

 lower, or clay-bearing members, of this series is shown. 



Subdivisions. — The Clay Marl series can be subdivided as fol- 

 lows, the divisions being numbered from base upward : 2 



1 In an earlier report of the Survey (1892), the base of the Clay Marls as 

 mapped by Dr. W. B. Clark, include 90 or more feet of interbedded black 

 clay and lignitic sand, exposed between Cheesequake creek and Matawan 

 creek. These beds should more properly be classed with the Raritan forma- 

 tion for the following reasons: a) they are nonglauconitic ; b) they are 

 -extremely variable and individual beds cannot be traced any distance ; c) 

 they contain a flora which connects them with the underlying rather than the 

 overlying beds, and d) the clay layers, some of which are massive beds, thin 

 out to the southwest and give place to sand, until in the vicinity of the 

 head of Cheesequake creek the Clay Marl series is underlain by 90 feet of 

 loose white sand with comparatively few beds of black clay. If the clays 

 east of Cheesequake creek are included in the Clay Marl (Clark's Matawan 

 series), the base of the latter is not drawn at a constant geological horizon, 

 but rises or falls as the upper portion of the underlying series of beds is 

 sandy or clayey. 



2 These subdivisions were first made out by Mr. Knapp and mapped by 

 him in 1893-1895. The following names were at that time suggested by him 

 for these divisions, beginning at the top (V) Wenonah sand, (IV) Marshall- 

 town clay, (III) Columbus sand, (II) Woodbury clay, (I) Merchantville 

 clay. 



