There is evidence of continued volcanism, with tuffs locally developed at various levels within the group. It was deposited in shallow marine conditions, consisting mainly of calcareous mudstones, siltstones, limestones and shales. The Dent Group is of latest Ordovician age and forms the lowermost part of the Windermere Supergroup. The transition from the top of the Borrowdale Volcanics into the overlying Dent Group is marked by an unconformity. The uppermost part is the Helvellyn Basin succession, consisting of volcaniclastic sandstones, dacitic lavas, andesitic lavas and tuffs, and dacitic ignimbrites. This is followed by the equally extensive Lincombe Tarns Tuff Formation, which is an ignimbrite. These are all followed by volcaniclastic sandstone of the Seathwaite Fell Sandstone Formation, which is developed over almost the whole outcrop, varying in thickness from 30 m to >1100 m. There are four main successions recognised at the base of the upper sequence: the Duddon Basin, the Scafell Caldera, the Haweswater Caldera and the Kentmere succession. The upper part of the group consists of mainly intermediate to acidic pyroclastic rocks and interbedded volcaniclastic sediments. The Birker Fell Andesite Formation makes up most of the lower BVG, varying in thickness from 980 m to 2700 m. In the southwest at Millom Park the Whinny Bank Tuff Formation is the lowermost unit, overlain by the Po House Tuff Formation. In the Furness Inlier the Greenscoe Tuff Formation is the lowermost unit. Locally in the western part, the lowest formation is the non-volcanic sandstones of the Latterbarrow Formation. The lower part of the succession is dominantly andesitic. In terms of chemistry, the BVG are moderate to highly potassic calk-alkaline in type.

It is further subdivided into many formations, of which only a few have regional extent. It is subdivided informally into two parts known as the Lower Borrowdale Volcanic Group and Upper Borrowdale Volcanic groups. It consists of a thick sequence of basaltic, andesitic, dacitic and rhyolitic lavas and pyroclastic rocks with interbedded volcaniclastic sediments. It is similar to, but distinct from, the Eycott Volcanic Group. The Borrowdale Volcanic Group (BVG) lies unconformably above the Skiddaw Group, and is of Caradocian age. The collision reached its end during the Early Devonian, part of the Acadian Orogeny with the final closure of Iapetus and the intrusion of late orogenic granites.

As the collision progressed the Lake District area became part of a foreland basin in which the Windermere Supergroup sediments were deposited, initially interfingering with the volcanics and then overlaying them. Continental collision began near the end of the Ordovician as southward subduction ceased and northward subduction beneath the margin of Laurentia began, forming the Southern Uplands accretionary wedge. This magmatism produced both the Borrowdale Volcanic Group sequence and the older granitic intrusions, which are the preserved magma chambers to the volcanics. Initial deepwater sedimentation recorded by the Skiddaw Group was followed by the development of a continental arc caused by the subduction of Iapetus oceanic crust beneath the Avalonian margin. In early Paleozoic times the area was on the northern margin of the microcontinent of Avalonia, which was moving northwards as the Iapetus Ocean began to close.

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