BASIC VOLOANICS OF HEMLOCK FORMATION. 117 



of scliistosity is noticeable. Tlie matrix between tlie ellipsoids varies very 

 much in degree of scliistosity, color, and composition. 



The most schistose, and b}' far the most common -\-ariety, is the dark 

 green matrix, which consists essentially of chlorite, epidote, and zoisite. 

 This material is clearly the result of the chloritization and the epidotization 

 of the original basalt constituting the ellipsoids, for we see it alternating 

 with bands of and grading into the less altered basalt. (PI. XL) 



A second facies of the jnatrix is that which possesses only a moderate 

 degree of scliistosity, and appears at times almost massive. This matrix may 

 be light colored, alm(>st white or greenish, or a dark bluish-black. It is 

 ■edium grained or aphanitic. The light-colored matrix consists essentially 

 ( it quartz and calcite. When a little chlorite or epidote is present, it has a 

 greenish tinge. The very dark variety consists of quartz and siderite, col- 

 ored with minute particles of iron oxide. The quartz-calcite or quartz-siderite 

 aggregates owe their origin to essentially the same jJi'ocesses, calcification, or 

 sideritization, respectively, followed by silicification of the original basaltic 

 material. They are therefore briefly described together here. Their charac- 

 ters and origin will be found discussed in detail on page 130 et seq. Some 

 of the peculiar characters of this matrix are illustrated in fig. B, PL XXVII. 



The least common variety of matrix found between the ellipsoids is of a 

 hglit greenish-gray or brownish color, and possesses a noticeablv brecciated 

 character (fig. B, PI. XXXIV, and PI. XI), but witli at the same time a certain 

 degree of scliistosity. Its characters are best seen under the microscope by 

 moderate magnification. Its brecciated character is then well shown. 



The fragments of such a matrix are of all sizes and are ang-ular. They 

 show quite commonly a separation into zones. The fragments now consist of 

 chlorite and epidote, and in the fragments with zonal arrangement chlorite in 

 exceedingly fine flaky aggregates occujDies the center and epidote the out- 

 side. Now and then there ma}' be several alternating zones of chlorite and 

 epidote. In all cases both epidote and chlorite are present in the zones, but 

 the one mentioned is in great quantity, while the other is ver}- subordinate. 

 The epidote is very commonly the dark ferruginous kind mentioned on 

 yage 101, and marks off the outer limits of the fragments. Now and 

 tlien the limits are outlined by a zone of brownish ferruginous material, 

 whose exact character could not be determined. The fragments of the 

 breccia show now neither original minerals nor textures. To judo-e from 



