Bullard, Edward;Everett, J.E.;Smith, A. GilbertPhilosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences,258,1088,28-10-1965,p.41–51. Bibcode: 1965RSPTA.258...41B. DOI: 10.1098/rsta.1965.0020.
Holmes, A.Transactions of the Geological Society of Glasgow,18,3,01-01-1931,p.559–606. DOI: 10.1144/transglas.18.3.559.
Bullard, Edward;Everett, J.E.;Smith, A. GilbertPhilosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences,258,1088,28-10-1965,p.41–51. Bibcode: 1965RSPTA.258...41B. DOI: 10.1098/rsta.1965.0020.