TRUCK SOILS. 345 



beyond the reach of the tides, is normally too small to have much 

 influence upon vegetation is indicated by the researches of Massart 

 on the Belgian coast. The following analysis of sand-strand soil is 

 given in his paper: 1 



Hydroscopic water 0.22 



Free water .28 



Substances soluble in water .02 



SOLUBLE IN NITRIC ACID. 



Iron oxide .14 



Alumina _ . .. .13 



Calcium carbonate . .14 



Magnesium .14 



Carbon dioxide ... .12 



SOLUBLE IN SULPHURIC ACID. 



Alumina _ .30 



Phosphoric acid Traces. 



Insoluble ._ 98.81 



100. 00 



Despite its excessive permeability, the soil is here rarely dry except 

 at and very near the surface. Even on the dunes one can easily reach 

 moist sand with his hands. Near tide level, as everyone knows, the 

 shallowest depression soon fills with water. Tt is probable that only 

 the smallest plants of this strand formal ion ever have difficulty in 

 reaching a sufficient supply of water with their roots. Abundant 

 deposition of moisture in the form of spray, rain, and dew, and the 

 resistance to evaporation offered by the superficial layer of the sand, as 

 well as by the abundant atmospheric humidity, are factors which suffi- 

 ciently account for this, at first glance, somewhat anomalous condition. 

 A further physical peculiarity of sand which is of interest in connec- 

 tion with the vegetation is the rapidity with which the surface layer 

 absorbs a great amount of heat, while the moist underlying portion 

 remains always eool. On the other hand, sand gives up its heat with 

 equal rapidity. Consequently it receives after nightfall a heavy pre- 

 cipitation of dew. 



THE PLAIN— TRUCK SOILS. 

 GENERAL OBSERVATIONS. 



That part of the Dismal Swamp region which belongs neither to the 

 strand, the salt marshes, nor the wooded swamps we have designated 



' Mem. Soc. Roy. Bot. de Belgique 32, pt. 1 (1893) ; quoted from Swaelmens " Le 

 boisement de la cote beige" (1888). 



'•' In the following publications of the Department of Agriculture Professor Milton 

 Whitney has quite fully described the peculiarities of the so-called "truck" soils 

 that occur along the Atlantic coast in the United States: Yearbook for 1S94, pp. 

 129 to 143 (1805); Bui. No. 5. Div. Agr. Soils, pp. 15, 16, pis. 12 to 18 (1896); Bui. 

 No. 13, Div Agr. Soils, pp. 8 to 11 (1898). 



