Dr H.R. Ellis Davidson in her Gods and Myths of Northern Europe, 1964 (in my opinion the best book of its kind in the last 51 years) points out that there is an association between Thor and fire. She states that in the Kjalnesinga Saga that there is a description of a temple dedicated to Thor in which there is an "altar made of iron on top":
"This was the place for the fire which was never allowed to go out. This they called the sacred fire."
Some scholars dismiss this description as an invention purely on the grounds that the saga is a 'late' on. Dr Ellis Davidson though considers the association of fire with Thor to be genuine and I am inclined to agree with her. She offers as supporting evidence the fact that a perpetual fire burned in the temple of Perkunos, the Thunder God of the Old Prussians, in an oak tree sanctuary. The oak as my readers will know is sacred to all of the Indo-European Thunder Gods, especially here in Northern Europe (with exception of Iceland) and the tree itself plays such an important part in the mythology and spiritual life of heathen England and Germania.
Thor as lord of the lightning is thus the lord of the fire from heaven. In her book she gives us a good description of the practices of the Old Prussians in respect of Perkunos:
"The chief of these sanctuaries was at Romove, where there was a holy oak, in whose trunk were placed images of the gods. Before that of the thunder god, Perkuno, was a fire which was never allowed to go out. The fire was surrounded by curtains, forming a shrine which only the high priest might enter to commune with Perkuno. The name of this god is linked with the Latin for oak, quercus, and it is probable that Donar too was worshipped in sanctuaries of this type. In England there are a number of Anglo-Saxon place-names in the form of Þunre leah, the meaning of which is 'grove, or forest clearing of Thunder.'"
Interestingly Dr Ellis Davidson draws our attention to the existence of a grove dedicated to Thor that still existed until the year 1000 CE on the north bank of the river Liffey outside Dublin when it was destroyed by King Brian Boru. However it took him a month to complete its destruction so this must have been a sanctuary on a grand scale.
The oak tree of all trees of the forest is the most susceptible to be struck by lightning and thus we have an association between fire and the oak, both of which are sacred to Thor.
"As a channel through which the power of the sky god might reach down to the world of men, it is understandable that the mighty oak tree, itself a splendid symbol of age, strength, and endurance, came to be considered specially sacred to the Thunderer."
In a sense the oak tree acts as a conductor of Thor's lightning power and thus a medium of not only His power which fills us with awe of Him but it is a way that He can most powerfully communicate with us. The study of Baltic mythology and heathen religious practice should be of importance to us as Germanic heathens for they give us insight into the beliefs and practices of our ancestors. Germany had a number of Donars Eichen (Donar's Oaks) but the most famous of these was located in Gaesmere in the state of Hesse. This sacred oak was cut down by the servants of the Anglo-Saxon missionary Boniface in the year 723 or 724, an act of sacrilege and religious and cultural vandalism.
"Now at that time many of the Hessians, brought under the Catholic faith and confirmed by the grace of the sevenfold spirit, received the laying on of hands; others indeed, not yet strengthened in soul, refused to accept in their entirety the lessons of the inviolate faith. Moreover some were wont secretly, some openly to sacrifice to trees and springs; some in secret, others openly practiced inspections of victims and divinations, legerdemain and incantations; some turned their attention to auguries and auspices and various sacrificial rites; while others, with sounder minds, abandoned all the profanations of heathenism, and committed none of these things. With the advice and counsel of these last, the saint attempted, in the place called Gaesmere, while the servants of God stood by his side, to fell a certain oak of extraordinary size, which is called, by an old name of the pagans, the Oak of Jupiter. And when in the strength of his steadfast heart he had cut the lower notch, there was present a great multitude of pagans, who in their souls were earnestly cursing the enemy of their gods. But when the fore side of the tree was notched only a little, suddenly the oak's vast bulk, driven by a blast from above, crashed to the ground, shivering its crown of branches as it fell; and, as if by the gracious compensation of the Most High, it was also burst into four parts, and four trunks of huge size, equal in length, were seen, unwrought by the brethren who stood by. At this sight the pagans who before had cursed now, on the contrary, believed, and blessed the Lord, and put away their former reviling. Then moreover the most holy bishop, after taking counsel with the brethren, built from the timber of the tree wooden oratory, and dedicated it in honor of Saint Peter the apostle."
This act of heinous sacrilege was repeated time after time in Germania and we are reminded of Karl the Butcher's destruction of the Irminsul at Heresburg in Nordrhein-Westfalen in 772 CE during the Saxon Wars. Both Donar's Oak and the Irminsul were types of representations of the world tree Yggdrasil.
In Songs of the Russian People (1872) by William Shedden Ralston we have this interesting observation:
"In Lithuania Perkunas, as the God of Thunder, was worshipped with great reverence. His statue is said to have held in its hand a 'precious stone like fire', shaped 'in the image of the lightning', and before it constantly burnt an oak-wood fire. If the fire by any chance went out, it was rekindled by means of sparks struck from the stone."
The Lapps worshipped Thor who was known to them as Horagelles (Old Man Thor) or Toora/Taara in Estonia and Torym to the Ostyaks. In a 17th century engraving of a Saami sacrificial site Horagelles has a long handled hammer, and nails in the head. Suspended from the nail is a flint which the God can use to make fire. This reminds me of the story of the whetstone stuck in the forehead of Thor after his duel with the giant Hrungnir in Skldsakaparmal in the Younger Edda. As an interesting aside Wulf Ingessunu in his latest book Ar-Kan-Rune-Lag. The Secret Aryan Way (2015) associates this stone with the rune Stan and alludes to the Graal Stone which fell from the Light-Bearer, Lucifer's crown.