In this Chapter, Dr Heddle discussed the substances usually thrown together, under the term of Chloritic Minerals. He showed, by an extensive series of analyses, that they were to be divided into three groups—those which occurred in metamorphic rocks, in recent strata, and in volcanic rocks.

He proposed to confine the term Chloritic to the minerals which are found in metamorphic rocks, and to apply the term, the Saponites, to those which occur in volcanic rocks.