7. Plan of vault on intersecting arches 21 8. Section of an intersecting arch 22 9. Plan of a bay in the nave of St. Maurice at Angers 24 10. Transverse section of the nave of St. Maurice at Angers 25 11. Plan of a bay of the nave. Ste. Trinité, Laval 26 12. Section of two bays of the nave. Ste. Trinité, Laval 27 13, 14. Comparative sections of Churches of Angoulême and Angers 28 15. View in perspective of nave vault. St. Maurice at Angers 29 16. Plan of a summer of the nave vault. Ste. Trinité, Laval 30 17. Plan of one of the nave piers. Ste. Trinité, Laval 30 18. Plan of the nave, St. Maurice, Angers 33 19. Plan of La Ste. Trinité, Angers 34 20. Section of a bay. Ste. Trinité, Angers 35 21. Transverse section of a bay. Ste. Trinité, Angers 37 22. Section of a single-aisled Church vaulted on intersecting arches with buttresses 38 23. Section of a three-aisled Church vaulted on intersecting arches with flying buttresses 39 24. Durham Cathedral. Transverse sections 43 25. Abbey Church at Noyon. Plan 44 26. Transverse section of Noyon Church 45 27. Church of Tournai, Belgium. Exterior view of north transept towards the Scheldt 46 28. Monastery Church at Moissac. Vault of the hall known as the _Salle des Capitaines_ above the porch 47 29. Church of Tournai, Belgium. Interior of north transept 47 30. Soissons Cathedral, south transept. Section of flying buttress 48 31. Perspective view of south transept, Soissons Cathedral 49 32. Cathedral of Laon. Plan 52 33. Cathedral of Laon. Interior of the nave 54 34. Cathedral of Laon. Main façade 55 35. Cathedral of Laon. The east end 57 36. Cathedral of Laon. Section of the nave 58 37. Notre Dame de Paris. Plan 59 38. Notre Dame de Paris. Section of the nave 60 39. Notre Dame de Paris. Flying buttresses and south tower 61 40. Sens Cathedral. Plan of a bay 62 41. Sens Cathedral. Section of a bay of the nave 63 42. Sens Cathedral. Interior 64