▁prepar ation ▁for ▁agricult ure ▁( field ▁stones ) ▁but ▁many ▁also ▁from ▁stone ▁quar ried ▁nearby . ▁For ▁modern ▁walls , ▁quar ried ▁stone ▁is ▁almost ▁always ▁used . ▁The ▁type ▁of ▁wall ▁built ▁will ▁depend ▁on ▁the ▁nature ▁of ▁the ▁stones ▁available . ▁ ▁One ▁type ▁of ▁wall ▁is ▁called ▁a ▁" double " ▁wall ▁and ▁is ▁constructed ▁by ▁placing ▁two ▁rows ▁of ▁stones ▁along ▁the ▁boundary ▁to ▁be ▁w alled . ▁The ▁foundation ▁stones ▁are ▁ide ally ▁set ▁into ▁the ▁ground ▁so ▁as ▁to ▁rest ▁firm ly ▁on ▁the ▁sub so il . ▁The ▁rows ▁are ▁composed ▁of ▁large ▁fl att ish ▁stones , ▁dimin ishing ▁in ▁size ▁as ▁the ▁wall ▁r ises . ▁Sm aller ▁stones ▁may ▁be ▁used ▁as ▁ch ock s ▁in ▁areas ▁where ▁the ▁natural ▁stone ▁shape ▁is ▁more ▁rounded . ▁The ▁walls ▁are ▁built ▁up ▁to ▁the ▁desired ▁height ▁layer - by - layer ▁( course ▁by ▁course ) ▁and , ▁at ▁intervals , ▁large ▁tie - st ones ▁or ▁through ▁stones ▁are ▁placed ▁which ▁span ▁both ▁faces ▁of ▁the ▁wall ▁and ▁sometimes ▁project . ▁These ▁have ▁the ▁effect ▁of ▁bond ing ▁what ▁would ▁otherwise ▁be ▁two ▁thin ▁walls ▁lean ing ▁against ▁each ▁other , ▁greatly ▁increasing ▁the ▁strength ▁of ▁the ▁wall . ▁Dim in ishing ▁the ▁width ▁of ▁the ▁wall ▁as ▁it ▁gets ▁higher , ▁as ▁tradition ally ▁done ▁in ▁Britain , ▁also ▁strength ens ▁the ▁wall ▁consider ably . ▁The ▁void s ▁between ▁the ▁facing ▁stones ▁are ▁carefully ▁pack ed ▁with ▁smaller ▁stones