THE SCOPE OF ECONOMIC GEOLOGY 9 
horizonta] fissures due to the shrinkage of the rock during 
cooling, The floors are arranged like the rungs of a ladder, 
and such lodes are called ladder-lodes (Fig. 3). The typical 
®Xamples are at Wood's Point in Victoria, where they 
Occur in dykes of hornblende-porphyrite in slate. As a 
fule the floors of a ladder-lode are confined to the igneous 
tock ; but where on solidification that rock froze firmly to 
the adjacent slate the shrinkage cracks and consequently 
‘he quartz-floors extend into it. 
Contra-lodes (Fig. 4) are small lodes which cross a lode at 
a high angle, just as great faults are crossed by secondary 
Cross-course faults. If some lode material has been deposited 
along a cross-fault it is a metalliferous cross-course or contra 
Cu 
¥ 
Cus 
F16. 3.—A LADDER-Lopg, F16. 4—A ConTra-Lobk. 
A ladder-lode in a dyke traversing A contra-lode (Pb) containing 
slate. In two cases the quartz- lead, formed along a fault 
floors are shown penetrating which has broken a copper 
along cracks into the slate. lode {Cu). 
lode ; if the cross-course be only filled with clay it is a cross- 
fluccan. Great faults may extend to depths of probably 
a hundred miles, and the fissure lodes doubtless extend far 
below the levels which can be reached by mining ; and 
some lodes, or series of associated lodes. may extend for 
hundreds of miles in length. 
Lodes are usually much longer than their thickness ; 
but those formed along the intersection of two fractures or 
in a solution channel are pipe-lodes or * ore chimneys,” as 
the Achilles lode of gold ore at Tarradale, Victoria, or the 
Harrington-Hickory Mine in Utah due to the replacement of 
limestone along a cross fissure by lead ore (Butler, USGS. 
Prof. Pap., 111, 1920, p. 517). 
Lodes in folded sedimentary strata are often isolated. and