1920.] NATURAL SCIENCES OF PHILADELPHIA 115 



Acidities of the Soils of the Different Geological Formations. 



For the purposes of the present study the geological formations 

 may be grouped into: Cretaceous, Miocene, Pensauken, Cape May, 

 and Recent. The Cretaceous strata, which outcrop toward the 

 western side of the region, are made up of sand, clay, marl, glau- 

 conite, and fossil shells. Salts of calcium, potassium, etc., are rela- 

 tively large in amount in the water extracts of the soils ; and there is 

 enough calcium carbonate present in most of the beds to neutralize 

 any acids which develop in the soils, so that circunineutral reaction. 

 is the rule. 



The Miocene consists of gravel and sand beds, which were raised 

 above sea level soon after their deposition, and have remained so 

 practically ever since. As a result of long-continued weathering 

 most of the calcium and potassium salts, as well as any calcium 

 carbonate the beds may originally have contained, have been leached 

 out. Acids arising from the decomposition of humus or from any 

 other source remain un -neutralized, and mediacid reaction is present 

 nearly throughout the areas underlain by Miocene formations. In 

 the deeper parts of the soil, however, the acidity diminishes, being 

 as low as minimacid at depths of a few decimeters; and the banks 

 of streams, road cuts, etc., occasionally expose low acid material. 



The sand and gravel classed as the Pensauken formation, with 

 which the Bridgeton is here included, is believed to have been derived 

 by erosion of the Miocene, and the soils of the two are practically 

 identical in the respects under consideration. 



The Cape May formation consists of sand and clay of late Qua- 

 ternary age, deposited by streams swollen by water from the great 

 ice sheet, which reached nearly to the northern edge of the present 



^Hollick, Arthur. The relation between forestry and geology in New Jersey. 

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Stone, Witmer. The life areas of southern New Jersey. Proc. Acad. Nat. 

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The plants of southern New Jersey, with especial reference to the 



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Harshberger, John W. Phytogeographic survey of North America, 790 pp. 

 Leipzig, 1911. 



The vegetation of the New Jersey pine-barrens. An ecologic 



investigation. 329 pp. Philadelphia, 1916. 



Taylor, Norman. On the origin and present distribution of the pine-barrens 

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Floi'a of the vicinity of New York. A contribution to plant 



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