The succession and structure of the Borrowdale volcanic rocks Northwest of Ullswater

The succession consists of Skiddaw Slates followed by Borrowdale Volcanic rocks (Ordovician) and is very similar to that previously described southeast of Ullswater (Moseley 1960). The Ullswater Group, more than 4000 ft thick forms the lowest part of the volcanic succession and consists of tuffs, basalts, basic andesites, and andesites. Above this about 1000 ft of the rocks of the Birk Fell Group, which are dominantly felsitic, are exposed. Important structural elements are the Ullswater Anticline, the Ullswater Thrust and the high angle faults. The anticlinal axis follows Ullswater as far as Glencoynedale and can be demonstrated only in the Borrowdale Volcanic rocks. The anticline does not appear to continue downwards into the Skiddaw Slates which are not only of different tectonic facies to the volcanics, but are separated from them by the southeasterly dipping Ullswater Thrust. This thrust was induced by the disharmony between the competent volcanics and the incompetent Skiddaw Slates, and is thought to be an imbricate thrust complex rather than a single dislocation. The high angle faults, the third important structural element, have northwest, northerly and westerly trends. It is probable that the northwesterly faults, at least, are wrench faults, although a strike slip component can be demonstrated in one instance only. The nature of the movement of the northerly and westerly faults cannot be ascertained.