280 Reviews—The Igneous Rocks of Encownter Bay. 
a series which was adequate in 1870 is no longer as representative 
as is desirable. Thus, while nets of the commoner simple forms of 
the cubic system are given, those of the important trapezohedral 
form of this system—the pentagonal icositetrahedron and the 
tetrahedral pentagonal dodecahedron—are lacking. Similar lacune 
are found in the tetragonal and rhombohedral systems. No cubic 
combinations are given, and the nets of oblique and anorthic crystals 
illustrate a nomenclature now obsolete and could be profitably 
replaced by others representing actual crystals of common substances 
such as orthoclase, gypsum, and copper sulphate, belonging to these 
systems. It is to be hoped that the publishers of this series may some 
day see their way to giving us a revised and extended set of nets 
fully illustrative of modern crystallography. 
4 
Tue Iagneous Rocxs or Encounter Bay. By W. R. Browne. 
Trans. Roy. Soc. 8._Australia, vol. xliv, 1920. pp. 1-57, with 
4 plates. 
HIS communication is an important contribution to igneous 
petrology, and adds a distinct chapter to the history of igneous 
action in South Australia. 
The igneous rocks of Encounter Bay comprise two related series, 
(a) a plutonic series, consisting of quartz mica diorite, adamellite, 
potash granite, and albite mica syenite, and (6) a series of minor 
intrusions consisting of uralitic dolerites, potash aplites, soda 
aplite, and granophyre. The whole asemblage of rocks is to be 
regarded as a plutonic complex, the component members of which 
have been successively and more or less independently injected into 
their present positions from an underlying magma reservoir. The 
sequence of intrusion in the plutonic series is (1) quartz mica diorite, 
(2) adamellite, (5) potash granite, (4) albite mica syenite, the last- 
named rock being considered as an end product of differentiation. 
The facts of intrusion are best explained as due to a differentiation 
brought about in the underlymg magma basin by fractional 
crystallization with sinking of crystals. 
The suite of minor intrusions is considered as derived by 
complementary differentiation from a magma of composition 
closely comparable to the dominant adamellite type. The aplitic 
members of this complementary suite are completely free from 
ferromagnesian minerals. An interesting feature of the soda aplites 
is the development of a chequer twin structure in the albite felspar, 
a characteristic which appears to be widely developed in rocks of 
this class. 
The plutonic complex is intrusive into a series of Lower Cambrian 
(or possibly late pre-Cambrian) sediments, which at the visible 
contact with the intrusive rocks are pelitic in character. The 
intrusions are considered to have accompanied the diastrophic 
movements which put an end to the Cambrian sedimentation. 
