NEWARK ROCKS OF ROCKLAND COUNTY, N. Y. 19 



numbers in the conglomerate layers. They are not everywhere 

 present in equal numbers at equal distances from the border, nor 

 in the same horizon. Locally they form almost the entire mass 

 of the conglomerate beds, and here the largest fragments are 

 always found. No sharp lines can be drawn between 1) the con- 

 glomerates made up almost entirely of limestone, 2) those con- 

 taining limestone pebbles with an equal or greater number of 

 sandstone, quartzite and quartz pebbles and 3) those which con- 

 tain no limestone at all. Even were the bed rock everywhere ex- 

 posed, it is doubtful whether such differentiation could be made. 

 Every gradation between conglomerate composed essentially of 

 limestone pebbles and conglomerate with no limestone is ap- 

 parently present. The gradations occur not only in successive 

 horizons from east to west, but apparently along the strike of the 

 beds. The localities where the limestone phase of the conglom- 

 erate is most marked are all close to the northwestern border of 

 the formation, but not all the beds along this border are equally 

 calcareous. Some of them contain comparatively little limestone. 



The limestone fragments have usually a reddish or bluish tinge 

 and are often somewhat angular or but slightly rounded. Bould- 

 ers several feet in diameter have been seen surrounded by a mass 

 of smaller fragments, the whole being bound together by a red 

 mud cement. Where purest, the rock has been quarried and 

 burnt for lime. In appearance it resembles exactly the famous 

 Potomac marble, found at Point of Kocks (Md.) 



Similar calcareous conglomerates are known to occur at a num- 

 ber of places in New Jersey. They are always located near the 

 northwestern border of the formation, as is the case in New York. 

 So far as known, limestone does not always occur along the 

 border, where these conglomerates are found. In no case however 

 in New York was it possible to prove that a narrow strip of lime- 

 stone might not be present between the conglomerate and the 

 gneissic and granitic rocks of Eamapo mountain. If present, it 

 must be in many cases an exceedingly narrow strip. The entire 

 absence of any gneissic or granitic pebbles in these conglomerates, 

 though they are in some cases only a few hundred yards from 



