I found a period review of each of the two books contained within this volume, Caves of the Earth and Mines and Mining (see below the description). This antique binding would make them a great gift for a geologist – the Victorian thirst for natural history makes them an interesting read, too, I bet.
Caves of the Earth; Their Natural History, Features, and Incidents. London: Religious Tract Society, n.d. (1847) bound together with N/A. Mines and Mining. London: Religious tract Society, n.d. (1851). 16mo. , 2-192, , iv, , 6-192,  in 3/4 green leather over navy taffeta covered boards, titles, etc. gilt-stamped to spine, green eps. Cover edges worn a bit, spine and top edges cover tanned. P.o.n. inked top right ffep, else pages clean with minimal aging. Science ECB10037 $75.00
[Review images are of the entries for these books in Reviews and Literary Notices in Wesleyan Methodist Association Magazine for 1848, volume the eleventh. London: R. Abercrombie. p. 24 and Reviews and Literary Notices in Wesleyan Methodist Association Magazine for 1851, volume the fourteenth. London: Association Bookroom. p. 284]