The paratectonic Caledonides in the British Isles consist of a Cambrian through Devonian mobile-belt sequence with great vertical and lateral facies variations. The main climactic deformation, metamorphism, and intrusion of granite in the paratectonic belt occurred in late Silurian time; Lower Devonian cyclothemic redbed sequences bear a molasse relation to the granite, although earlier movement phases are recorded in numerous--generally local--unconformities. Major structure is generally simple regional cleavage, and fold axial surfaces are steep and buckled; slicing and flattening of the sedimentary pile was related closely to movements in the basement. Horizontal shortening values derived from flattening across cleavage range from 50 to 80 percent, whereas vertical ext nsion was from 150 to more than 400 percent. Flattening and cleavage development generally were preceded by buckling, which adds an additional shortening increment. Complex sequences of strain are superimposed, producing intricate fold-facing and fold-plunge geometry; however, in most regions, sequential bulk strains of vertical extension followed by axial extension, vertical shortening, then axial shortening, occurred. Further complications in strain were induced, particularly in North Wales, by Ordovician volcano-tectonic domes.