This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
55. Footing courses built on slopes - especially of clay - are always likely to slide; this may be avoided by cutting horizontal steps in the slope as shown in Fig. 17, where the slope e f is stepped off, as shown at a, in order that the footings b may have a horizontal bearing. These footings may be of either stone or concrete, but when the former material is used, great care must be exercised to secure a perfect bond at the stepping places, and the foundations should be laid in as long sections as possible.