I haven't had access to this treasure for some seven years, and that was before I became an "official" "historian" (whatever that means). It did not lose its shine. Although I had been enthralled with her history (particularly the Dutch theory of Figure's origins, having noted the similarities between Morgan and Friesian skulls and legs the first day I met a Morgan), I had been more focused on her exacting and uncompromising descriptions of conformation, correct movement, and proper handling.
Her standards were precise, with detailed descriptions, invaluable illustrations, and firm ethics that are sometimes hard to see at horse shows (in any breed or discipline!), as good trainers are often quiet and the questionable ones are often the loudest.
But, back to the history! The True Briton (Thoroughbred) theory of Figure's (Justin Morgan, the Horse) parentage, I believe, gained traction because of it's inclusion in Joseph Battell's 1894 Morgan Horse Register. However, even Battell presents the idea as hearsay. Re-reading Mellin's book gave me enough information to do some further digging, and I found this (see page 12) from 1879. I highly recommend Morgan history enthusiasts read the whole article (it is delightfully and entertainingly written!), but here are some key points: Justin Morgan (the owner, not the horse) did have True Briton at his farm for two seasons, and his nearby cousin for one. However, all three seasons were several years prior to Figure's conception. The article then sets out that "Young Bulrock," a Dutch horse (presumed from the Hudson colonies), who stood at Church's farm the year before Figure's birth, and being the only nearby Dutch stud advertised, must logically be the sire of the sport colt whom Justin Morgan himself referred to as a Dutch horse.
"If the Justin Morgan's pedigree be corrected in the third vol. of the Trotting Register*, it may be hoped that the parrot ing second-hand stock journals will, some time in the far future, cease to inform the everlasting enquiring correspondent that 'Justin Morgan was sired by True Briton, dam a Wildair mare.'"
Wallace's Monthly: An Illustrated Magazine Devoted to Domesticated Animal Nature, Volume 5 (1879), pg 14
Sadly, the far future has not yet come.
*in the days before the foundation of the Morgan Horse Club, and indeed here before Battell's landmark Register, many horses of Morgan breeding were registered as Trotters.