For creating "mountains", usually igneous volcanic rocks, rugged mountain rocks with sharp edges, are used. Smooth, rounded sedimentary rocks are used for the borders of gravel "rivers" or "seashores." In Chinese gardens of the Song dynasty, individual rocks which looked like animals or had other unusual features were often the star attraction of the garden. In Japanese gardens, individual rocks rarely play the starring role; the emphasis is upon the harmony of the composition. For arranging rocks, there are many rules in the "Sakuteiki", for example: