


238 STRUCTURAL AND FIELD GEOLOGY 
Width and Extent of Lodes.—Individual lodes often 
vary much in width—the walls of the fissure approaching 
and receding in an irregular manner, and now and again 
being in close apposition, in which case the lode is, of course, 
“nipped out.” Such irregularities, it need hardly be said, 
are due to the character of the original fissure, except when 
limestone forms the wall or walls of a lode. In such cases 
the irregular width of the cleft has not infrequently been 
caused by the unequal dissolution of the rock. Some lodes 
are very narrow—a few feet or less—others may exceed 100 
feet in width. In the case of very broad lodes, however 
(say, from 20 feet to 100 feet), it must be understood that 
this is not the actual width of the original fissure, but includes 
as much of the adjacent rock as contains ore in payable 
quantity—whether occurring as impregnations or as strings, 
threads, veinlets, and flats (see pp. 252, 255). Some broad 
lodes, for example, consist of more or less numerous and 
approximately parallel veins, occupying very narrow fissures 
or mere cracks, which in the central portion of the “lode” 
are often less than an inch apart, but become more widely 
separated towards the limits of the fissured area. Lodes of 
this kind are known as “sheeted zones,’ and sometimes 
attain a width of 100 feet or more. A “sheeted gameu 
therefore, is simply a belt of highly fissured rock, which, 
when gold is present in the fissures, may be profitably 
extracted so long as the veins are rich enough or sufficiently 
numerous. 
Lodes differ considerably in length or lateral “extemn 
Some die out in much less than a mile, while others have 
been followed for great distances. Probably the longest 
known is the auriferous “ Mother Lode” of the Sierra Nevada, 
California, which runs in a relatively straight line for more 
than 70 miles. 
The longest veins seem usually to have the greatest 
vertical range. Some of these have been followed to depths 
not far short of 3000 feet, without showing any appearance 
of dying out. Many of the shorter veins wedge out down- 
wards or upwards. Lodes of this kind are frequently very 
irregular—branching often in many directions. Some wedge 
out simply ; others, again, divide into two or more smaller and 

