Com Clinometer 6z6x3g

COM CLINOMETER

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COM CLINOMETER

(Contd.)

The Brunton com was originally designed by a Canadian geologist named D.W. Brunton, and built by William Ainsworth Company in Denver, Colorado.

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The Brunton® com is used by more geologists for field mapping of geological objects

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Detailed measurement of geological objects, such as fold, Faults, ts- hinge line, axial line, axial plane, geological mapping, & plane becomes essentially impractical without the use of the com

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This instrument consists of a large circular dial with three concentric graduations

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The outermost peripheral graduation reads from 0o to 360o clock wise for reading full circle bearings.

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The inner most graduation indicates the geographic directions for reading quadrant bearings. In this the positions of E and W are reversed with reference to the N for easy and direct reading as in g the instruments is turned about its com needle which always points to the North.

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The third graduation is in between the above two in the lower half of the dial and is semicircular reading from 0o at W to 90o either side towards N and S indicating dip values in degrees.

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A large magnetized com needle with its n-end marked and a pendulum are pivoted at the centre co-axially which move freely on the graduations of the dial.

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The whole assembly is enclosed in a circular non-magnetic aluminum box with a glass top mounted on a tilting stand with sight slits. The stand acts as a base for the clinometers and sighting devise for the com bearings. Outside the box there is an arresting pin to stop the movement of the com needle.

COM CLINOMETER

(Contd.)

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The pendulum is used to the determination of dip of rock beds, of ts, fault plane.

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The free movement the magnetic needle and the pendulum can be stopped with the help of an arresting key on the body of the instrument.

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The instrument is provided with bridge, which can be rotated about NorthSouth axis of the dial and kept vertical when the equipment is in used as a com.

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It is also used as clinometers (i.e. to determine the amount of dip of an inclined surface)

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The bridge lies in with the instrument rests on the inclined surface obviously at this position, the dial lies in a vertical plane if base lies parallel o the direction of maximum slope of the inclined surface.

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At this position pendulum oscillate freely and its pointer reads the amount of slope of the plane.

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The amount of dip is expressed in degrees like 30o, 40o etc The direction of dips expressed also in degree with two geographic directions like N30oW, S60oE

COM CLINOMETER (Contd.) PROCEDURES FOR THE MEASUREMENT OF THE AMOUNT OF DIP • Direction along which the amount of dip is to be measured • If the surface of the rock is not even a book may be placed and above the book the stand of the com clinometers is allowed to rest. • The pendulum is allowed to move freely by loosing the screw.

• If the bed is horizontal the pendulum rests on South which is vertically downward the amount of dip is 0o. • If the bed is inclined it moves away from the South and comes to rest in some position the reading is taken to the position. • • This is the amount of dip. In this way the amounts of dip are taken in several direction the greatest among these amount may be taken as true dip.

COM CLINOMETER (Contd.)

PROCEDURE FOR THE DETERMINTATION OF THE DIRECTION OF DIP

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While standing in the field two permanent or semi permanent objects are selected, such as temple, hills, Church.

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Hold the com clinometers in such a way North of the diark inside the direction of the objects, then loosen the screw and allowed the magnetic needle to move freely.

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The magnetic needle moves and comes to rest the North of magnetic needle, always points towards North. Whether North of the dairy is towards the right of North end of magnetic needle or towards left.

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Takes the readings North of the dark and North of Magnetic needle let us say 20o.

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If the North of the diark is 20o towards the right of the object is N20oE from you and you are S20oW form the object.

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Similarly readings are taken with reference to another object then lines are drawn on the top sheet the point of intersection of two lines with the point where you are standing.

COM CLINOMETER

(Contd.)

MEASUREMENT OF STRIKE DIRECTION A safe & suitable point is selected on or near the outcrop and the comclinometers with its base brought over the dial is held in the hand at the eye and sighted through the slits in the direction of the strike from the south end (Sometimes the edge of the bedding, ts etc which are parallel to the strike direction and coincides with the line of sight. FIG pp56 fig7.4 stru geo sathya narayanaswami The Com-clinometers may also be held in the hand firmly at the waist level the base along or parallel to the strike direction and leveled. In some cases the edge of the com base may be held firmly pressed against the bedding surface in the direction of strike and the com leveled. Next when the com needle comes to rest it is arrested and reading taken from the N-point of the dial towards east or west and recorded as N25oE, N40oW etc, or commonly N25oE, S25oW etc.

COM CLINOMETER

(Contd.)

MEASUREMENT OF DIP Direction of Dip- The direction of the dip of the beds is determined by similar methods as explained above by holding the com -clinometer length wise in the direction of dip. The direction should always be read from the N- or S point of the dial towards East or West and recorded as N30oE, S70oW etc. Amount of Dip – as the same observation point or at a nearly edge of the dipping strata a clean even surface is selected and the com-clinometer is placed on it and held firmly with its length in the direction of dip. Immediately the pendulum moves on from its rest position 0o and comes to rest on a point on the dip value scale. The reading is taken then from the position of the pendulum on the scale and recorded in degree as 23o,25o,etc.