Gould 1903, p. 179 Gould, I. Chalkley (1903). "Carl's Wark". Journal of the Derbyshire Archaeological and Natural History Society. 25. Derby: Derbyshire Archaeological and Natural History Society: 175–180. Retrieved 12 February 2011.
Gould 1903, pp. 178–179 Gould, I. Chalkley (1903). "Carl's Wark". Journal of the Derbyshire Archaeological and Natural History Society. 25. Derby: Derbyshire Archaeological and Natural History Society: 175–180. Retrieved 12 February 2011.
Gould 1903, p. 175 Gould, I. Chalkley (1903). "Carl's Wark". Journal of the Derbyshire Archaeological and Natural History Society. 25. Derby: Derbyshire Archaeological and Natural History Society: 175–180. Retrieved 12 February 2011.