After House-Mary Roberts Rinehart

Penniless Leonard Outram attempts to redress the undeserved loss of his family estates and fiancee by seeking his fortune in Africa. In the course of his adventures he and his Zulu companion Otter save a young Portuguese woman, Juanna Rodd, together with her nursemaid Soa, from slavery. Leonard and Juanna are plainly attracted to each other, but prone to bickering, and their romance is impeded by the watchful and jealous Soa. The protagonists seek the legendary People of the Mist, said to possess a fabulous hoard of jewels. Finding them, they immediately become embroiled in the turbulent political affairs of the lost race, which is riven by a power-struggle between the monarch and the priesthood of its giant crocodile god. The heroic Leonard can do little more than react to events. The action climaxes in a hair-raising escape by toboggan (it was a flat stone) down a steep glacier. (Summary by Wikipedia)