Gall and Curl on a Horse Chestnut leaf

Whilst walking from Amberley to Arundel in West Sussex, UK, I spotted an abnormal growth on a leaf in a tree near the River Arun... I think it was a horse chestnut (Aesculus hippocastanum), but I do not remember now.  There were a collection of these on a few leaves here and there.  I suspect one would find some kind of mite inside... I left them undisturbed...

Also on the same tree was a curled leaf...