

256 STRUCTURAL AND FIELD GEOLOGY 
lenticular spaces to occur between adjoining beds in the cores 
of the anticlinal and synclinal folds. These spaces subse- 
quently filled with quartz form the so-called “saddle-reefs.” 
Each reef is thickest along the middle line or axis of a fold, 
the anticlinal reefs tapering off downwards, and the synclinal 
reefs upwards, There would seem to be a succession of such 

FIG. 102.—DIAGRAM-SECTION TO SHOW THE GENERAL STRUCTURE OF 
‘‘ SADDLE-REEFS.”’ 
a, a, anticlines ; s, s, synclines ; d, d, dykes. 
reefs occurring one above another, at greater or less intervals, 
the anticlinal reefs being more frequent and better developed 
than those occurring in the synclinal cores. At Bendigo, 
narrow dykes of dolerite are associated with the reefs. The 
reefs carry native gold and auriferous sulphides in small 
grains and particles, as well as sharply angular fragments of 
the country-rock. 
[The famous Broken Hill silver lode of New South Wales is, according 
to Pittman, another example of a bedded “saddle-reef.” Broken Hil! 
itself is a low range composed of various schistose rocks, forming an 
anticline, the axis of which coincides with the crown of the range. The 
back of the great saddle-reef, before it was exploited, formed the crest 
of the range for a mile and a half, but it has now been nearly all quarried 
away, the open cut varying in width from twenty to one hundred feet. 
It was composed mainly of massive manganiferous limonite, yielding 
certain percentages of silver and lead. Throughout this mass many 
cavities (vughs) occurred, containing crystals of carbonate of lead 
(cerussite), chloride, iodide, and chloro-bromide of silver, and stalactites 
of psilomelane. Underneath this gossan or “‘iron-hat” a thick zone of 
so-called ‘‘oxidised ores” and native silver was encountered, the zone 
yielding variable but often very high percentages of the precious metal. 
