"A search was conducted on his crutches and 20 stones of hashish were found in each stick, making 40 stones."
To me this is an impossible weight to store in crutches,how much in weight was the drug? or in other words what is the weight of a stone in Gambia? Anyway the long and short of the matter is that I think that it is unlikely that the convicted man will be able to pay the fine of D1&1/2 Million.
Wikipedia here tells you about the normal interpretation although in its history it has varied,in the UK before metrication came about a stone in weight was 14Lbs,each pound being 16 ounces in weight