The Snowstorm by Beryl Netherclift.
 
For Caroline, Kit and Richard, as well as their dog, Chunky, the prospect of staying with Aunt Amethyst at Farthingales, her old house on the edge of the Devonshire moors, was an exciting one. As Caroline said after-wards, I don't know how it was but I knew at once something was going to happen through that door ... And something did when they discovered the antique paperweight, a snowstorm, on the library mantelpiece.
 
Farthingales Manor was fast falling into disrepair and Aunt Amethyst had to spend most of her time trying to maintain it. The children, though, could see that it was a losing battle and unless something happened soon Farthingales would no longer belong to the Faradays. It was the snowstorm that told them about the legendary Farthingales collection of antique coins, or rather it was through the snowstorm that they learnt about it, for the glass globe certainly possessed peculiar properties. Then the mysterious paperweight disappeared and the children began to learn about snowstorms of another kind.
 
This unusual and attractively written book will appeal equally to boys and girls, and especially to those blessed with imagination and a sense of adventure.