in the case of steeply dipping planes is recorded with a small arrow for direction upon the map. When the fault plane is flat-dipping, the strike of the striæ is given. Brecciated material within the fault walls should be carefully studied, since fragments may have been dragged from some formation not represented on the present surface, and so give an idea as to the amount of movement which has taken place. Again the cementing material and its relation to the fragments may give a clue as to the history of the movement, and may be possible to determine whether it has taken place by successive stages or not.

When a fault or fissure shows mineralization it is a vein, and it becomes necessary to determine whether it is of productive or non-productive type. In many cases this cannot be done until one is familiar with local conditions and has seen portions of the different vein types developed. In the examination of a vein the geologist should note all the recognizable minerals and select specimens for the determination of those which cannot be identified in the field. He should find out as far as possible the order in which they formed-later minerals cut the older ones, or cement fragments of them, or are deposited in the layers of regular cavity filling further from the walls, unless there has been a later reopening of the fissure. Minerals usually occur in certain groups or associations (see p. 130), and this will sometimes help in the recognition of doubtful specimens, or may give an indication as to what may be expected in a certain portion of a vein. It is well to take samples of the vein material while doing the field work to gain some idea of the values and to serve as a basis for recommendation as to systematic prospecting and sampling. Hand specimens of vein material should be taken and kept for reference in the office, especially when the relations between the minerals are not clear to the unaided eye in the field. These may afterward be examined in thin section, or with polished surfaces, with the microscope; in this way otherwise obscure bits of vein history are made clear. (Reference: "The Microscopic Examination of Opaque Minerals," by William Campbell, Economic Geology, Vol. I, No. 8. Also "A Micro

scopic Examination of the Cobalt Nickel Arsenides and Silver Deposits of Temiskaming," by W. Campbell and C. W. Knight in the same number of Economic Geology. "On the Microstructure of Nickeliferous Pyrrhotites," same authors, Economic Geology, Vol. II, No. 4.)

In the mapping of all productive outcrops, great care should be taken to represent as graphically as possible the exact outline of the outcrop, if necessary, even exaggerating it somewhat in width for the purpose of bringing out relations clearly and indicating the relative importance of the different portions. Variations in width, branches, and intersecting fractures, even if apparently insignificant, should be plotted, since they may bring out causes contributory to the formation of the more important bodies. Alterations of the country rock peculiar to the localities of the ore bodies may be recognized and traced to other bodies which at first glance show no relation to the original set. As an example of this, ore bodies of the "chimney type" have been found to occur along belts connected only by zones of discolored country rock, and developing as a result of intersections with cross leads of apparently unimportant character. By drifting along such a zone as determined by the surface mapping, ore bodies with no outcrop have been located.

The structural features, such as folding, fracturing and shearing, and the character and extent of alteration of the country rock, should be carefully observed in the neighborhood of the ore bodies; any connection between the two may be of importance. For instance, fracturing and shattering along the axis of a fold may produce conditions especially favorable to ore deposition; impermeable beds confine the circulation of transporting solutions, etc.

Field Notes. An invariable rule for the geological observer should be "Do it now." When he sees anything he should put it down either on his map or in his notes, else he may lose it, for the chances are against returning to a locality once visited, unless there is a strong feeling of having missed something. Then, too, there is always the advantage of having a concrete expression of

an idea such as a note or sketch to refresh the memory or to compare with later ideas.

FIG. 25. This cut shows part of a working sheet, and illustrates the manner of recording as much data as possible on the map. The dotted areas represent outcrops of ore bodies, which are usually inked in red on the field sheets.

Upon the field map (see Fig. 25) should go the data, all of it, that may conveniently appear there, such as notes of the minerals

Lucky Strike Mine- Surface Notes

Aug 12th 1905

No.1-No. 1, specimen of relatively fresh monzonite typical
of this locality. Shows quite abundant plagioclase
and a good deal of biotite.

315 N.
235 E

340 N.
237 E.

No. 2-No. 2 is more siliceous phase of this rock, quartz and
orthoclase quite noticeable, some mica. Small veinlets
of pegmatitic quartz are numerous in this locality.
No. 2 a quartz-mica diorite(?)

No. 3-Limestone-monzonite contact, some contact metamorphism.
chiefly on the limestone side. Specimen No.3 is contact
metamorphic rock, chiefly brown and green garnet and
vesuvianite. Noted some wollastonite (?) apparently
later than the garnet. There are also iron stained places
along this contact, suggestive of magnetite contact.

390 N.
250 E.

390 N. 250 E. to 450 N. 275 E.

In this locality there is a good exposure of the Ls-Mcontact.
which is elsewhere largely wash covered. In general, the
metamorphic action does not seem to have been great. It
is confined to the contact; zone ranges from 3'to 7'in
width. Metallic minerals scant. Noted magnetite, garnet
Fluorite, vesuvianite, horne.

FIG. 26. This shows the method of keeping notes to supplement the mapwork; reference to points on the map is made by giving the coordinate locations.

in veins and contact zones, which may be referred to by abbreviations of their chemical formulas. Vein and fault widths should be noted, and the line followed in traversing should be indicated; vein types should be distinguished by colors. More or less generalized representation is desirable for areas showing alteration or disseminated mineralization.

In addition to the notes upon the map the pocket note-book is used for sketches and descriptions; specimens and samples are described and their numbers, with the map coördinates or locations, are entered on the left margin of the page (see Fig. 26).

FIG. 27. This figure is taken from a sketch in a field note book; it is fairly typical of several which were made in studying the structure along this section.

In this book are made sketches of structural features, or sections (Fig. 27); any unusual or interesting thing, such as a case of fault displacement, or a vein formation, is so recorded. Ideas regarding the different problems encountered are jotted down; and every once in a while it is well to go over these ideas and take stock of them, summarizing and arranging for use in further investigation and in the writing of a report.

It is the business of a geologist in investigating an area to