62 Quaternary Formations of Southern New Jersey. 



By these two lines of approach, therefore, we seem to reach 

 different conclusions with reference to the height of the Bridge- 

 ton plain at Hightstown. 



Possible changes of level. — If the Glassboro phase of the 

 Bridgeton formation is glacial outwash in part, it filled the broad 

 valley from Amboy to Bordentown, and overspread the low 

 divide below Berlin. On the lowland bordering the Delaware, 

 some 50 feet of Bridgeton material accumulated, and 50 feet 

 more on the divide at Glassboro. It would appear, therefore, 

 that the Bridgeton material must have been something like 100 

 feet deep, at a maximum, on the lowland along the Delaware. 

 The upper surface of the deposit at Haddonfield must have been 

 at a level which is now somewhere about 200 feet above the sea, 

 and there should have been a harmonious gradient from Hights- 

 town toward Haddonfield sufficient to allow the transportation 

 of material, if it came by way of the Hudson, and if relative 

 levels have not changed since. This would bring the Bridgeton 

 surface at Hightstown up to the supposed pre-Bridgeton plain 

 of erosion at Freehold, about 200 feet; but this level at Free- 

 hold did not receive the glacial outwash. Therefore we must 

 infer either that the preceding hypotheses are incorrect, or that 

 the relative altitudes of the Freehold and Glassboro regions have 

 changed. Evidence of relative change is found in the fact that 

 the Bridg"eton formation, reaching an elevation of 200 feet 

 (present) at Berlin, appears not to have reached the 200-foot 

 areas at Freehold, though the latter place is some 50 miles nearer 

 the assumed source of the gravel. Allowing for the necessary 

 gradient, it would seem that the Freehold region should have 

 stood 100 feet or so higher than the Berlin region at this time, 

 in order to have escaped deposition. 



From data about Berlin, it is concluded that that region stood 

 80 to 100 feet lower in Bridgeton time than now. If this was 

 the case, the Freehold region might have had an altitude similar 

 to that of the present. 



It is difficult to conceive what the attitude of the region was 

 in Bridgeton time, in order to meet all requirements. If the 

 region near Hightstown and Freehold was elevated at the be- 



