rock
data frame has 48 rows and 4 columns.Twelve core samples from petroleum reservoirs were sampled by 4 cross-sections. Each core sample was measured for permeability, and each cross-section has total area of pores, total perimeter of pores, and shape.
data(rock)
Katz, R. (1995) Spatial Analysis of Pore Images. D.Phil. thesis, Department of Statistics, University of Oxford.
Venables, W.N. and Ripley, B.D. (1994) Modern Applied Statistics with S-Plus. Springer-Verlag.