The toad is the opposite of air, it is a contrary element, namely earth
The opposites and their symbols are so common in the texts that it is superfluous to cite evidence from the sources.
On the other hand, in view of the ambiguity of the alchemists’ language, which is “tarn ethice quam physice” (as much ethical as physical),
it is worth while to go rather more closely into the manner in which the texts treat of the opposites.
Very often the masculine-feminine opposition is personified as King and Queen (in the Rosarium philosophorum also as Emperor and Empress), or as servus (slave) or vir rubeus (red man) and mulier Candida (white woman); in the “Visio Arislei” they appear as Gabricus (or
Thabritius) and Beya, the King’s son and daughter.
Theriomorphic symbols are equally common and are often found in the illustrations.
I would mention the eagle and toad (“the eagle flying through the air and the toad crawling on the ground”), which are the “emblem” of Avicenna in Michael Maier, the eagle representing Luna “or Juno, Venus, Beya, who is fugitive and winged like the eagle, which flies up to the clouds and receives the rays of the sun in his eyes.”
The toad “is the opposite of air, it is a contrary element, namely earth, whereon alone it moves by slow steps, and does not trust itself to another element. Its head is very heavy and gazes at the earth.
For this reason it denotes the philosophic earth, which cannot fly [i.e., cannot be sublimated], as it is firm and solid. Upon it as a
foundation the golden house is to be built. Were it not for the earth in our work the air would fly away, neither would the fire have its nourishment, nor the water its vessel.” ~Carl Jung, CW 14, Para 2