The foundation of the Cathedral is of Maine granite. Although the bed-rock of Morningside Heights (Manhattan schist) lies near the surface, it is so disintegrated near the top that it was necessary to go down 72 feet in some places in order that the Cathedral might rest securely on the “living rock.” The excavation and foundation alone cost a quarter of a million dollars. The main walls of the superstructure are also of granite, faced on the outside of the finished portion with Mohegan golden granite quarried near Peekskill, N. Y., and on the inside with a soft buff-colored limestone or dolomite called Frontenac stone from Pepin county, Wis. The great flying buttresses and massive piers of the Crossing, exposed in their rugged unfinished state, exhibit the dark Maine granite. Local materials are mentioned in their appropriate places. Exterior Survey Before entering the Cathedral the visitor should make a circuit of the Close (beginning on the south side and going eastward), comparing the outlines of the Cathedral with the plan and noting the location of the other buildings. This will give him a better understanding of the interior of the Cathedral and of its ultimate connection with the Bishop’s House and the Choir School by means of cloisters. It will be noted that the Old Synod House (brick, with Ionic-columned portico) occupies the site of the South Transept. =The Seven Chapels of Tongues=, (see page 69 et seq.,) may be identified on the exterior by the following characteristics (south to north): _Chapel of St. James_, rectangular plan, crenelated parapet of roof, and pinnacles on buttresses. _Chapel of St. Ambrose_, half round window arches. _Chapel of St. Martin of Tours_, fleurs de lis in quatrefoils above large windows; narrow pointed arch windows with single lights in basement. _Chapel of St. Saviour_ (easternmost), rectangular plan; cross on gable; statues in niches of buttresses and wall. _Chapel of St. Columba_, angel on roof; statues in niches of buttresses. _Chapel of St. Boniface_, statues in niches of buttresses; small mullioned windows of three lights in basement. _Chapel of St. Ansgarius_, rectangular plan; parapet of quatrefoil tracery; pinnacles on buttresses.