I'll ask my dad although he is quite busy just now and not as young as he used to be (infact its his birthday today) and it is a bit of a trek up there, however i'm going up to scotland in july so could try and have a look myself (i haven't been up craig phadrig since i was small ) i assume you mean check out what the ramparts are made of. There are geological maps of the area for the natural stuff . the field club in Inverness often writes about stuff like this so they may have more information ( infact my mum and dad attend some of there meetings so could maybe find out more from them.)My concern about going up there is obviously the ramparts are all covered in grass and i wouldn't like to dig about as i'm not qualified in any way to do so. But i could try and get some photos and see what is there,exposed if anything.Hopefully i will have time.
I also felt they must have used ladders to get in, making it quite safe from intruders.
love
carolinexx