The contributors and myself gathered their effort and knowledge to produce the present volume when it was decided that IGCP project 453 would have its second field meeting in Sion, in the midst of the western Swiss Alps. Therefore, this guide-book presents 6 field trips which are at the programme of the meeting. The field trips are divided in two sections corresponding to the Alpine Externides and Internides, allowing the visitors to get a good overview of the entire western Swiss Alps.
The theme of IGCP 453 is: Uniformitarianism revisited: a comparison between modern and ancient orogens, under the leadership of Brendan Murphy and Duncan Keppie. lt was obvious then, that a good share of basement geology should be included in the guide, and two field trips (Ftl and Ft5) are mainly devoted to Variscan and pre-Variscan rocks outcrops.
We felt that it was also necessary to present in such a document the latest ideas on Alpine and pre-Alpine geology of the western Tethys realm. Parts of recent publications were used for that matter, they were updated, and put in a general introduction with numerous figures, mainly devoted to the geodynamics of this area in space and time.
Coloured Alpine cross-section and block diagram, and excerpts of the new 100 '000 structural map of Western Switzerland have been put in annex, in a pouch on the back-cover. Similar excerpts of the topographie map of Switzerland, on which stops are located, accompany each field trip.
Making a guide-book for such a geological monument as the western Swiss Alps is quite a challenge ... and obviously the present guide is presenting only a small part of what can be seen in this area of the Alps. We hope you will enjoy visiting our mountains, and hopefully get some insights on the fascinating geological history hidden behind those magnificent land history hidden behind those magnificent landscapes.