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and of types intermediate between these, was established at the time that Rosenbusch's book appeared. In this year (1877) Törnebohm^[1] suggested that the name hyperite to be used for the latter class, composed essentially of plagioclase, diallage and an orthorhombic pyroxene, that the term gabbro should be used to designate plutonic rocks in which the pyroxene is diallage, and that hyphersthenite (or norite) should be restricted to those containing a rhombic pyroxene as their principal augitic constituent. This suggestion has not met with a very wide acceptance because the gradation between the three types is very gradual, and in all cases the geological relations of the types are the same. It is convenient, however, as a descriptive name for those gabbros containing two pyroxenes.

In the same year Streng^[2] investigated the crystalline rocks of Minnesota and described a gabbro from near Duluth, in that State, to which he gave the name hornblende-gabbro, because of the supposition that the brown hornblende it contains is primary. Irving,^[3] however, has shown that much of the brown hornblende in the rocks of the Lake Superior region is secondary. He thought that nearly all, if not all, of the hornblende of the hornblende gabbros is of this nature. Williams^[4] has also shown that compact brown hornblende is often a secondary product of the alteration of augite; and Wadsworth^[5] holds to the view that this is the character of all the hornblende in the Lake Superior gabbros.