The settlers who followed the traders into this country also made use of the trees which grew along the streams, but as settlement began to penetrate the unforested interior of the State the earth itself provided building material for frontier homes. A furrow some three inches deep was plowed into a tough sod containing many grass roots, and the broken sod was cut into lengths the width of the wall, up to two and a half feet. One row of blocks was laid lengthwise of the wall and the next crosswise, with the joints staggered as in laying bricks. The finished wall provided a strong, thick barrier against summer heat and winter cold. The roof, like that of many log houses, was of poles covered with brush, often finished with overlapping strips of sod. Sometimes these sod roofs actually bloomed in the spring as their many roots came to life, and one pioneer told of the small poles which formed the framework of his roof leafing out inside the house in midwinter. Improved transportation brought lumber into North Dakota, and frame shanties and houses were built. The red barn took a prominent place on the farm, and the silo, for storing fodder, reared its vertical mass, sometimes dwarfing even the windmill its revolving silvery fins. Except for the more affluent farms, where the homes sometimes boasted as many as 12 rooms and a porch, the farmhouses followed an uninspired cycle of rectangular or L-shaped frame structures, often with a lean-to shed at the back for storing wood or coal. On Russo-German farms in the southern and western parts of the State a European love of color asserted itself as houses were painted sky blue or nile green or pink, and color combinations such as red, white, and blue formed a pattern of diagonal stripes on the barn or granary door. In each township appeared the one-room country school, usually white or light green in color, with its three windows on each side, coal shed and door in one end, chimney and black board in the other, and possibly a bell tower over the door. The early school was not only a seat of learning, it was also the community center, where a Saturday night basket social might be followed by church services the next morning.