An A-Z of Modern America by Alicia Duchak, 1999.
The burial of the heart away from the body. This is a very ancient practice, the special reverence shown towards the heart being doubtless due to its early associations with the soul of man, his affections, courage and conscience…. Some of the most notable cases are those of:
An Illustrated Encyclopedia of Traditional Symbols by J.C. Cooper, 1978.
The Concise Oxford Dictionary of Proverbs by J.A. Simpson, 1982.
Besides the enormous diversity of combinations and the mathematical fascination with cards, it is a curious fact that the four designs are all symbols of life. The spade is derived from the leaf, the heart is the source of life, the diamond or lozenge is a symbol of the yoni or female principle and the club is the trefoil, one of the most ancient symbols of the Trinity or the three-fold aspect of life.
Ancient Pagan Symbols by Elizabeth Goldsmith, 1929.