The silica-poor vulcanic rocks of the Inner Hebrides are the hostrock for whitish-greyish Agates. More intensively colours like a brownish-greyish tone are rare. Part of the pattern of these agates can be the “Onyx-agate” (“uruguay-agate-typus”) - so called from the local collectors.
Another well known agate variety from the isle of Skye is the so called “whorl-agate”. A typus of agate better known from other places as “cloud-agate”.
More informations about scottish agates are given in Dr.H.G. Macpherson´s book “agates” (published by the British Museum (Natural History) and the National Museums of Scotland).
You can find more informations about scottish agates on the following webpages:
Chris Harlows webpage about scottish agates
Nick Crawfords webpage scotsagate
H.Currie Minerals of Scotland