260 The American Geologist. April, 1894 
work phase. In fact, reticulated veins and veinlets, or stockworks, 
although a phase, also, of shear veins, may be regarded as in the main 
.1 sub-type of the gash veins. In calcareous rocks, the cracks have been 
very generally enlarged by solution, before filling; and in both calcare- 
ous and siliceous rocks impregnation and replacement of the walls are 
of common occurrence. The transverse fissures due to plication, here 
referred to gash veins, are likely to be limited in depth, and to differ 
from ordinary joint-cracks, chiefly in the divergence of the walls, di- 
verging downwards in sv nclinal cracks and upwards in anticlinal cracks. 
Among the manj more or less typical examples of gash veins which 
might be cited are the following: the auriferous pyrite and chalco- 
pyrite veins of Gilpin county, ( iolorado; the veinlets of native copper in 
felsite, Santa Rita, N. M.: and the lead and zinc deposits of the Missis- 
sippi valley, which take the form chiefly of gash veins and Hats, the 
flats being in part horizontal gash veins. As examples of stockworks 
in this country, we have the Black Copper group, Globe district, Ar- 
izona; the zinc deposits nl' the Saucon valley. Pennsy I van ia : the lead- 
silver deposits in the dolomite of Aspen mountain, Colorado; and. in 
part, the quicksilver deposits of New Almaden, California. 
id) Tnterbedded veins, filling rifts between the strata, i. <.. fissures par- 
allel with the strata and due io plication. Although the close relations 
of this type to the gash veins are very obvious, its distinctive features 
are so strongly marked as, in the opinion of the writer, to justify its 
separate recognition. In fact no type of vein possesses more definite 
characteristics or is more readily identified. As a rule, they conform 
closely or perfectly with the strata in strike and dip, present in many 
cases remarkably smooth and well-defined walls, without indications of 
slipping, and from the nature of the case they must be limited in depth. 
The essential thing is that thej are rifts due to plication, for of course 
true fissure veins (a) maj conform with the strata superficially. Tarr, 
in his recent and comprehensive work on the "Economic Geology of the 
United States" (p. 90), seems to consider that for veins of this type 
there were no pre-existing fissures, segregation commencing along a 
bedding plane, and the deposit as it grew crowding back the rocks and 
making room for itself, much as a concretion or a root might. That 
this is a possible explanation I am ready to believe, for I have observed 
something analagous in the veinlets of gypsum traversing anhydrite in 
the gypsum quarries of Windsor. Nova Scotia. But I have no reason to 
suppose that this action would be any more efficienl in the bedding 
planes than along joint or other cracks transverse to the bedding, and 
riffs between the strata are unquestionably a natural result of the fold- 
ing of thin-bedded rocks; although the 1 wo causes might, of course, co- 
operate, [f these trulj concretionary veins should prove to be impor- 
tant or of economic interest it would become necessan to make a 
fundamental distinct ion in the classification between endogenous veins 
(formed in pre-existing cavities) and exogenous veins (formed, like con- 
cretions, in the solid rock). As examples of interbedded veins, we have 
the auriferous quartz veins of Nova Scotia, California, and other <iis- 
