182 



That certain portions of this deposit may be rendered available 

 for enriching the soil, I firmly believe. The statement already 

 made, that there sometimes exists in it a considerable share of 

 the greensand, in other words, of the fertilizing material of the 

 marl, is enough to encourage those who possess it and not the 

 genuine marl, to give it their attention. Notwithstanding the very 

 frequent, we may say the almost invariable occurrence, of the 

 astringent matters, which are in themselves so unequivocally 

 deleterious to vegetation, certain precautions may be adopted, 

 such as must make it a valuable auxiliary to the farmer in places 

 where the genuine marl lies too remote. The recommendations 

 respecting the mode of using it, will be found in the chapter on 

 the economic geology of the greensand formation. 



This material alternates both with the lighter coloured clays 

 and sands already spoken of, and with the greensand, which it 

 overlies in some parts of Monmouth county. It is well exposed 

 for examination in the cuttings upon the Camden and Amboy 

 railroad. Containing occasionally a small proportion of the 

 green grains, and resembling somewhat, when moist, the true 

 greensand or marl, it is frequently applied to the soil through a 

 misconception of its true nature, to the serious detriment of the 

 crop. 



ECONOMICAL GEOLOGY. 



White Clay of Woodbridge. — About one mile southwest of 

 Woodbridge, near the level of a small stream on the road to New 

 Brunswick, there occurs an insulated deposit of white clay and 

 white sand, in which both materials are of remarkable purity. 



This local bed is surrounded by the red shale rocks of the 

 middle secondary series, and would seem to be a remnant of the 

 lowermost layers of the upper secondary group, lying in a de- 

 pression of the surface where it has escaped removal during the 

 general denudation of the strata. 



Beneath about ten feet of reddish diluvial matter, derived from 

 the adjoining red shale, we find a bed of pure white sand, re- 

 gularly stratified, and dipping gently westward. Its thickness is 

 about ten feet. This sand is much esteemed as an ingredient for 

 the manufacture of fire bricks. Underneath the sand lies the 



