G. D. Griffiths

British author. Full name Gordon Douglas Griffifths. As well as one hard to find Dartmoor set pony book he wrote another story set on Dartmoor about an abandoned kitten (Abandoned) and a story about a hedgehog (Mattie). He also I think wrote a history of Teignmouth.

Pony Books:

SILVER BLUE
(WORLD'S WORK 1970)
ILLUSTRATED BY ELSIE WRIGLEY
SUMMARY: A story of a strain of silver blue coloured wild ponies set on Dartmoor

Collectors info:
I don't think Silver Blue was ever reprinted and is therefore fairly rare, although there are usually one or two copies around. May not be cheap. The author's other animal stories are however much easier to find.