The mission as a frontier institution in the Spanish american colonies, by Herbert E. Bolton.

http://www.archive.org/details/missionasfrontie00boltrich

By the equator's snowy peak a record of medical missionary work and travel in British East Africa by E May Crawford

http://www.archive.org/details/equatorssnowype00crawuoft

The Spanish pioneers and the California missions.

http://www.archive.org/details/spanishpioneersa009682mbp