
ORE-FORMATIONS | 245 
portion of the veinstuff. The fragments are of all shapes— 
angular, subangular, or rounded—and some of them may show 
smoothed and striated surfaces. They vary also in size, from 
large blocks down to finely comminuted particles. The ores 
are irregularly distributed through the veinstone as grains, 
crystals, patches or bunches, lamine, threads and strings, 
often crossing and recrossing. Sometimes they assume the 
form of vertical or steeply inclined columnar or chimney-like 
aggregates, surrounded on all sides by lean or barren vein- 
stuff. Such rudely columnar ore-bodies are known as shoots. 
Or they may appear in the form of more or less regular 
plates and tabular sheets, disposed in parallel positions with 
similar plates of veinstone; or, again, they may occur as 
massive aggregates occupying the whole fissure to the exclusion 
of any veinstuff. On the other hand, ore may be entirely 
wanting in some parts of a lode, the fissure being either filled 
with veinstone and rock-rubble only, or closed by the apposi- 
tion of its walls. 
Structure of Fissure Veins.—(@) MASSIVE STRUCTURE. 
When a fissure is entirely filled with ore, or with crystallised 
or cryptocrystalline mineral matter containing ore dissemi- 
nated through it, the structure is said to be massive (see 
Fig. 87, p. 239). Galena (lead-ore), for example, is often met 
with completely filling fissures—crystallised veinstone being 
either entirely absent or occurring only as small inclusions in 
the ore, or as a meagre interrupted layer lining the walls. 
Auriferous quartz-veins are an example of the same struc- 
ture—the ore in this case being included in the quartz which 
wholly fills the fissure. 
(6) PLATY, LAMELLATED, OR BANDED STRUCTURE.—In 
this structure the ore and the veinstone are disposed in more 
or less sharply defined sheets or layers parallel to the walls 
of the fissures (Plate L. 1). This is the commonest kind of 
structure met with in lodes. The sheets are of very vari- 
able thickness, and may be few in number, in which case 
some or all may be relatively thick; or they may be 
numerous and all extremely thin—mere laminz of irregu- 
larly alternating ore and veinstuff. Now and again, how- 
ever, they are arranged symmetrically in pairs. The opposite 
walls may each be lined, for example, with a layer of quartz 

