| books.google.be (n.d.) https://books.google.be/books?id=QNC7AAAAIAAJ&pg=PA285&lpg=PA285&dq=adam+heber+mine&source=bl&ots=tbojkja4d-&sig=ACfU3U3Wtkhb-G0cglnxDkGM-ENjGVEqtA&hl=nl&sa=X&ved=2ahUKEwjNsN-9vNLpAhVB4aQKHV1XDRYQ6AEwDHoECAoQAQ#v=onepage&q=adam%20heber%20mine&f=false |