Memory is a valuable source for the historian, but it is also dangerously unreliable.
In some countries (Egypt for example) sewage is a valuable source of water.
(The human resources department, whatever else its failings, is a valuable source of market data in this regard).
In what remains one of the nation's poorest regions, the fare is a valuable source of income for the drivers.
This minnow, like many others, is a valuable source of food for fishes, birds, and other animals.
The Vita S. Euthymii ("Life of St. Euthymius"), by a contemporary, is a valuable source for Byzantine history.
His book is a valuable source for his contemporaries and contains excerpts from earlier biographies no longer extant.
It is a valuable source of information regarding the daily lives of slaves in central Louisiana, including the Christmas celebratory practices in slave culture.
His herald wrote a biography of Edward that is a valuable source of contemporary information; the manuscript has been translated as The Black Prince (1842).
Dandong is a valuable source of hard currency for North Koreans: most of those 20,000 workers are employed in garment, machinery and fish-processing factories in Dandong and neighbouring towns, often working 13-hour days.
Although a fine example of Islamic learning, in usefulness it does not compare to the bibliographic work in Arabic by Hacı Halifa (Kâtip Çelebi; died 1658), which is a valuable source for modern knowledge of literary history.
