8S 
ILLUSTRATIONS OF LODES OR MINERAL VEINS. 
Wall Cases 24 to 36. 
The ores or moralUterous minerals seldom oeeur distributed in iisetul 
quantity through large masses of the rooks whieh eompose the crust of 
the earth, but are found more or less eoueeutrated in repositories of 
various form. These are, either beds or layers which bear evidence 
of haviuir been made up, like the strata of eartliv miiierals, bv the 
deposition of sediment trom water, or they are repositories formed bv 
the tilling of cavities produced in the rock masses since their original 
consolidation. By far the more important of this latter class are the lodes 
or mifH'ral rehfs, the sources of most of onr ores of silver, copper, tin, 
and lead, of much of the gold, and some of the most valuable iron ores. 
Grouped here and there in numerous regions of the earth, and studied 
both for their power of producing wealth, and for the interest and 
beauty of their crystallized minerals, these repositories have for 
centuries been the subject of research and of philosophical v'^peeulation. 
Especially during the last eighty years has it been aiixionsly attempt-ed 
by description and comparison of the phenomena obi;erved in them, to 
reduce to rule and law the peculiarities and apparent anomalies of their 
occurrence and of their production of metallic contents.^ 
The notable eonnexion between the course or direction of the lodes 
and the minerals which they yield, as also the circumstances eonnected 
with the nature of the rocks Avhich they traverse, require for their 
elucidation the aid of irood geolonucal maps on a lame scale, but manv 
of their varieties of structure, and most of the special appearances which 
mark epochs of change, and thus bear evidence to the principal events 
in their history, are capable of being illustrated by specimens. It is 
with this object that several eases in this museum are occupied wiili 
examples selected chietly from our own, but partly from foreign mines : 
and since the lodes or veins, called after the several metals for wliicli 
tltey happen to be Avorked, most usually exhibit a variety of different 
minerals associated totrether, and are subject more or less to the same 
phenomena of a structural kind, the Avhole of the specimens are arranged 
in one series, whether thev are taken from A'ciiis which are called 
* 
copper, silver, or lead lodes, according to the I'reponderance in value of 
one or other of these metals, or Avhether from veins in wliich tsvo or 
more of them arc found in available quantity. 
A lode may be described as a mineral repository once a tissure, 
filled up with the products partly of mechanical and partly of 
chemical action. Whilst the average Avidth of Avorkable lodes may be 
from one to six feet, tliev occasionalh^ attain as much as 60 or 100 feet, 
and in other instances are only a few inches, or, as in the ease of certain 
till and auriferous A'eins or “ strings,” no thicker than the blade of a 
knife. In no country probably can a vein be pointed out Avhieh contains 
but one single metallic mineral; if for example, it be a silver lode, the 
^ The names of Werner, YOU "Weissenlnioli, Sehmidt, Freiesleben. Bisohof, Cotta, 
and W. Jor}* llenwood may he eited as some of the authors Avho have of late chiefly 
contrihuted hy their works to our knowledge of these subjects. 
