1. S. I. Andreev, Soils of the Chuvash Autonomous Republic, Vol. 1 (Cheboksary, 1971) [in Russian].
2. A. D. Arkhangel’skii, Geological Works in Penza Gubernia (Moscow, 1911) [in Russian].
3. S. A. Arkhipov, “On the lithological facies of chocolate-colored Khvalyn clays and conditions of their origin,” Byul. Komis. Izuchen. Chetvertichn. Perioda, No. 22, 63–72 (1958).
4. P. N. Berezin, A. D. Voronin, and E. V. Shein, “Physical basics and criteria of vertisolization,” Vestn. Mosk Univ., Ser. 17: Pochvoved., No. 1, 31–38 (1989).
5. A. Bessonov and S. Neustruev, “Soil-geological essay on the Novouzen district of Samara gubernia,” Pochvovedenie, No. 3, 307–350 (1902).