Bibliographical Notice, : - 485 
we find that most of the veins or lodes are true fissures, and do not 
iminish in richness as they are sunk deeper into the earth. All 
these lodes have more or less clearly defined walls; and some of 
them are quite remarkable for their smoothness and regulari rity. We 
assume the position that the filling-up of all thes e lodes or veins 
with mineral matter was an event subsequent to any change that 
may have occurred in the country rock. Now, if we look carefully 
at all the azoic rocks in this region, we shall find, more or less di- 
stinctly defined, depending upon the structure of the rock itself, two 
planes of cleavage, one of them with a strike north-east and south- 
west, and the othe er south-east and north-west. Beside these two 
sets of 7 pce there are in most cases distinct lines of bed- 
ding. The question arises, what relation do these veins hold to 
these lines of cleavage ? Is it not possible Hes they occupy these 
cleavage: -openings as lines of greatest weakness 
* [ have taken the direction of these two wh of cleavage-planes 
many ics with a compass, over a large area; and very seldom do 
they diverge to any great extent from these two di ections, north-east 
and south-west, or south-east and north-west. In some instances 
the north-west and south-east plane would flex around so as to 
strike north and south, and the other one so as to trend east and 
west; but this is quite seldom, and never occurs unless there has 
been some marked disturbance of the rocks. There are, however, a 
few lodes which are called ‘east and west lodes, and some ‘north 
and south.’ A few have a strike north-west and south-east, but 
are generally very narrow, and break off from the north-east and 
south-west lodes, are very rich for a time, and then ‘ pinch’ out. 
t would seem, therefore, quite possible that the north-east and 
south-west veins took the lines of cleavage in that direction as lines 
of greatest weakness, and that the north-west and south-east lines 
cross the other set, and that a portion of the mineral material might 
accumulate in that Medscape merely throw out this as a 
hint at this time, which I wi sh to follow out in my future studies. 
onally e 
purely eruptive ranges of the nor ibant. portion of the San-Luis valley 
seem to be composed of a series of minor ranges en échelon, with a 
trend north-east and south-west. But as soon as this range joins on 
to a range with a metamorphic or granitic nucleus, the trend changes 
around to north-west and south-east. Many of the ranges have a 
nucleus of metamorphic rocks, though the central and highest ndi 
tions may be eomposed of eruptive peaks and ridges. In this 
e igneous material is thrust up in lines of the same direction as Vibo 
trend. It becomes, therefore, evident that all the operations of the 
