English reference that I have been able to find is from the Oxfordshire naturalist, Plot, who in 1677 wrote that
"besides the Brontiæ [i.e. thunderbolts] of the Forreign Naturalists we have others, which here in England we call likewise Thunderbolts, in the form of arrows heads, and thought by the vulgar to be indeed the darts of Heaven."
This statement, (which seems to be the source of Walcott's remark), is the more remarkable since along with these arrowheads he identifies as Brontiæ the fossil echinoderms, to which reference has already been made. After speaking of selenites and other stones which he considered to be "some way related to the Celestial Bodies," Plot proceeds:—
"I descend next to such as (by the vulgar at least) are thought to be sent us from the inferior Heaven, to be generated in the clouds, and discharged thence in the time of thunder and violent showers: for which very reason, and no other that we know of, the ancient Naturalists coined them suitable names, and called such as they were pleased to think fell in the Thunder, Brontiæ; and those that fell in showers, by the name of Ombrice . . . [of which] we have several sorts in Oxford-shire."
I may also mention that Sir J. Evans gives the best account of their distribution I have been able to find. After describing their distribution in Great Britain and Ireland, he proceeds to give an account of their distribution on the Continent, giving examples from Brittany and other parts of France, Savoy, various parts of Scandinavia, (where celts inscribed with runes occur), Germany, Holland, Portugal, Italy, and Greece. In the last country they are called astropelekia, and Sir John states that, about 1081, the Byzantine Emperor Alexius Comnenus sent to the Emperor Henry III. of Germany, ἀστροπέλεκυν δεδεμένον μετὰ χρυσαφίου i.e. probably a celt of meteoric origin