Six argillaceous rocks, six sandstones, two kinds of tuff and two tuffaceous sandstones from various localities in Japan ranging Palaeozoic to Pliocene in age were deformed in the triaxial vessel under 1 to 2500 bars in confining pressure, at room temperature and in strain rate 3.5x10^-5/sec. All are dry sample and underwent compression test.
The strength of Tertiary argillaceous rocks increases in direct proportion to age. In sandstone the age is important factor for the strength, too. On the other hand, in tuff and tuffaceous sandstone, grain the size seems most important for the strength.
As the deformation changes ductile to brittle, the mode of fracturing does wedgelike fracture, singleplane of shear fracture, network of a lots of minute shear fractures, and to flow. The transitional line from the single shear fracture to the network shear fracture occur in lower ductility in both tuff and tuffaceous sandstone, higher in sandstone, and highest in argillaceous rocks.