APA

Perkins A., . (1939). Our natural resources and their conservation. London: Chapman & Hall, limited.

Chicago

Perkins A, . 1939. Our natural resources and their conservation. London: Chapman & Hall, limited.

Harvard

Perkins A., . (1939). Our natural resources and their conservation. London: Chapman & Hall, limited.

MLA

Perkins A, . Our natural resources and their conservation. London: Chapman & Hall, limited. 1939.