I recenty purchased a geological map of my island (the isle of man) from the BGS. Along with the solid, drift and magnetic maps, i've got a graviy anomaly map.
Im puzzled as I cannot work out what causes the highest gravity anomalies 40Mgal +. i assumed they were areas of mountains (ie thicker crust), but the mountains on the island are not in the area of greatest Mgal. could someone explain it for me? I've tried the internet, but its all too much physics for me, im just a humble geologist lol 
GeologyRocks