ij6 
In the ballast of ships arriving from various countries there are 
often introduced not only plants which are foreign to the district, 
but also rocks, minerals and clays. These are deposited on land 
surfaces, and must exercise considerable influence upon the growth 
of vegetation. The calciferous portions of the Boulder Clay form 
excellent soils, and also the lime deposits usually found in the 
Keuper Marl and the Waterstones. The Carboniferous Limestone 
of Derbyshire and North Wales is also extensively used for this 
purpose. 
Before concluding it is desirable to state that fuller information 
may be had by consulting Mr. G. H. Morton’s excellent book on 
the Geology of the Country around Liverpool , and also the maps and 
memoirs of the Geological Survey. 
