1. In a bowl, thoroughly combine cornmeal, brown sugar, and salt. Gradually stir in boiling water, then oil. Cool to lukewarm, about 30 minutes.
2. Stir in yeast, then whole wheat flour and rye flour. Stir in enough white flour to make a moderately stiff dough.
3. Turn out onto a lightly floured surface and knead until smooth and elastic, 6 to 8 minutes.
4. Shape dough into a ball. Place in a lightly greased bowl, turning once to grease ball. Cover and let rise in a warm place until double, 50 to 60 minutes.
5. Punch dough down, and divide in half. Shape into 2 loaves and place in 2 greased loaf pans. Cover and let rise in a warm place until almost double, about 30 minutes.
6. Bake the loaves at 375 degrees Fahrenheit for 45 minutes. If bread browns rapidly, loosely cover with foil after first 25 minutes.