I found the system I was referring to regarding secondary and tertiary elements, here:
Added it to Wikipedia as well.
The four seasons had their own element assignments.
Spring (wet becoming hot) - Air - Aries, Taurus, Gemini
Summer (hot becoming dry) - Fire - Cancer, Leo, Virgo
Autumn (dry becoming cold) - Earth - Libra, Scorpio, Sagittarius
Winter (cold becoming wet) - Water - Capricorn, Aquarius, Pisces
Hence, each sign had it's own assigned element, plus a secondary element from the [northern] season it was assigned to. For three of them, the seasonal element matches the sign's element, yielding a "pure" element sign.
The tertiary was the opposite of the secondary; where in the southern hemisphere, it was the opposite season.
What we end up with is (types by Interaction Style/Keirsey combination using first two only for north, and first and last for south):
Fire, Earth, Air: Saggitarius (ESTJ/ESTP)
Fire, Air, Earth: Aries (ESTP/ESTJ)
Earth, Water, Fire: Capricorn (INFJ/INTJ)
Earth, Fire, Water: Virgo (INTJ/INFJ)
Water, Earth, Air: Scorpio (ISFJ/ISFP)
Air, Water, Fire: Aquarius (ENFP/ENTP)
Air, Air, Earth: Gemini (ESFP/ESFJ)
Water, Water, Fire: Pisces (INFP/INTP)
Fire, Fire, Water: Leo (ENTJ/ENFJ)
Earth, Air, Earth: Taurus (ISTP/ISTJ)
Air, Earth, Air: Libra (ESFJ/ESFP)
Water, Fire, Water: Cancer (INTP/INFP)
(Of course, these type correlations to signs aren't practical).