HARPER: VEGETATION OF THE HEMPSTEAD PLAINS 265 
Although the soil is not particularly fertile, the proximity of New 
York City makes truck farming more or less profitable under 
adverse soil conditions, and also causes large areas to be used for 
residential purposes irrespective of soil. 
The topography is nearly flat, as in many other prairies, but 
the surface has a southward slope of about 15 feet per mile, 
which is rather steep for a prairie, though almost imperceptible 
to the eye. Several shallow valleys traverse the area in a general 
north and south direction, and a few of these are long and deep 
enough to have small permanent streams in them. The western 
slopes of the valleys are nearly always steeper than the eastern, 
possibly on account of the deflective effect of the earth’s rotation,* 
though the amount of erosion since the glacial period must be 
very small. 
Geology and soil. The whole area is underlaid by a mixture 
of coarse sand and siliceous pebbles, supposed to represent a 
glacial outwash deposit, the terminal moraine being just to the 
north. At any rate, it is very recent geologically. The ground- 
water level averages perhaps 30 feet below the general level of the 
uplands, which explains the dryness of most of the valleys and 
some of the peculiarities of the vegetation. 
The soil proper is very characteristic, consisting of brownish 
silty loam covering the gravel to a depth of about a foot, except 
in the valleys, where it is thin or wanting. A mechanical analysis 
of a sample representing the uppermost 10 inches, from two miles 
northeast of Hicksville, is reported in the government soil survey 
as follows: 
Per cent 
Gravel (2-1mm.);...... coco do e eee cee coer toes 2.70 
Coarse sand (1-.5 шіп.)............................. 8.06 
Medium sand (.5-.25 шп.).......................... 3.96 
Fine sand (.25—1 шп.)......................----... 4.88 
Very fine sand (.1-.05 шп.)......................... 8.96 
Silt (05-605 tm.) 222222... DEP кауын а ue ep шыла 49.20 
* See G. K. Gilbert, Am. Jour. Sci. 127: 431-432. 1884. wipe gs Jont, 
Elisha Mitchell Sci. Soc., 10: 26-32. 1893. C. F. Brooks, School Sci. ath. 
17: 517—521. 1017. 
f АП particles exceeding 2 mm. in diameter are discarded in these mechanical 
analyses, which probably does not make much difference in this particular case, but 
would make a great difference in the corresponding чазак For this reason 
subsoil analysis given at the same place is not worth copying. 
