How to Collect and Preserve Fossils ? | Geology

The below mentioned article will guide you about how to collect and preserve fossils.

It is well not to break into the deposit at first, but to search very carefully over the surfaces which are not overgrown, but have been exposed to the action of the rain, streams, or sea. These are spoken of as the weathered surfaces. In many cases fossils are more easily seen on a weathered than on a fresh surface.

If one is seen, the next thing to do is to extract it without damage, and to do this often requires experience, and experience is often gained with the loss of many specimens.

The field geologist must have a hammer, and so often needs a chisel that he had better always have one with him.

The hammer should have at the one end of its steel head a square-shaped section, and should taper to an edge at the other end. In general it should weigh between one and one and a half pounds. The length of its handle should depend on the weight of the head and its cross section should be such that it can be comfortably held in the hand. The section through the handle should be elliptical and not circular.

The handle passes through an elliptical hole in the head, and it is well to drive into the top of the handle two iron wedges about two-thirds of an inch long. The wooden wedges usually driven in are apt to dry and shrink, and then fall out.

The chisel can be an ordinary cold chisel and should be about 6 inches long.

Besides a hammer and a chisel the collector must start out with a satchel Of some kind—a school-boy’s satchel is very convenient—and in it should be placed plenty of news­paper in order that each specimen should be wrapped up and so prevented from rubbing up against another one and being damaged.

It is a great convenience to have a number of small brown Holland bags with one, so that all the fossils from one quarry or from one bed in a quarry can be kept apart.

If fossils or rock specimens are merely collected as objects of beauty, they can be wrapped in paper and carried home without further trouble. But if they are collected for any scientific purpose, one must write on the paper the place they come from, and then on unwrapping them at home one must label them with the name of the bed of rock from which they were extracted and the name of the locality from which they come.

If several fossils from one place are taken, it saves a great deal of time to wrap them up and put them in a Holland bag together with a slip of paper on which are the names of the rock and locality from which they all come.

In the cases of very small or delicate specimens it is often more easy to remove them with a knife than with a hammer, and it is well to have a few match-boxes or pill-boxes with one in which to put them. They should be packed in grass or cotton-wool to prevent their breaking.

When a fossil is seen near the edge of a rock it can often be removed by a sharp blow with the hammer. Do not hit too near the fossil, but try to break off some of the rock round it, and then trim the specimen down. It is usually best to carry back more rock than is needed with the fossil and finish the trimming-down process with a smaller hammer at home.

If no fossils can be seen on the weathered surfaces exposed to view, you should then try and find out which were the original planes of deposition of the material form­ing the rock. These can often be discovered by noticing the colour streaks in the rocks, or by seeing if there are lines of pebbles or grains of various materials in the deposit.

If these bedding planes, as they are termed, can be found, the hammer or the chisel must be used to split the rock along them, and then the faces so exposed should be examined. If the rock-face in an exposure is not a bedding plane, it should be searched for any small hollows, as these are often due to fossils which have been broken across and have had their interiors weathered out. Should such hollows be found the bedding plane in which they are can be exposed by hammering and searched for fossils.

But the actual rock of a cliff or of a quarry which is in place should not occupy the whole attention of the collector. The fragments of rock which have been broken off from the rock face should also be carefully searched and these very often contain specimens which are far more easily extracted than those which occur in the rock-face.

One should also investigate the walls close by which have been built of blocks taken from a quarry, but great care should always be taken to keep separate the fossils found in a wall from those found from a rock which is in place.

In clay deposits there are often found rounded lumps of a hard material; these are called nodules, and though they may show on their outside no trace of a fossil, it is well worth breaking them open, for they often have formed round a fossil which has been preserved inside them.

It is seldom advisable to entirely extract a fossil from the piece of rock in which it may be found if the rock is soft. It is generally better to take it home partly embedded and leave till later the complete laying bare of the specimen. This can be done with a knife or a sharp-pointed steel instrument, and should be done with very great care. An old tooth-brush is generally very useful for cleaning up specimens after much of the attached rock has been re­moved from them.

If a fossil is seen embedded in a hard rock not near any corner where a stroke with the hammer can break off a piece of the rock, then much time and patience must often be given up to its removal.

In this case the chisel is very useful; a deep groove must be cut by the chisel at some distance from the fossil, and so that the hollow completely encircles the shell. Then the chisel must be held more horizontally and a sharp blow on it with the hammer will usually bring off the fossil in the flake of rock enclosed by the groove.

The space inside a shell which was formerly filled by the body of the animal which inhabited it is usually filled either with the sand or clay in which it was embedded, or by crystalline material. Sometimes the shell has been entirely removed by solution in water which at some after time soaked through the deposit. The infilling material is then left and is called an internal cast. This has generally taken up the exact form of the interior of the shell and often shows exceedingly fine markings.

In the same way the rock material on the outside has taken the exact moulding of the exterior of the shell and is called the external cast.

Such casts should be collected as well as specimens of the shell, and in some cases casts are common where shells are almost unknown.

If a fossil is broken during its extraction, do not always throw away the pieces. Often they can be joined together with seccotine or some other cement, and quite a good specimen may thus be preserved.

The naming of a specimen is often a matter of great difficulty. The best way is to consult geology books and compare your specimen with those figured in such books; or if a geological museum is in your neighborhood, take your specimens there and compare them with those in the museum.

In the case of fossils from a hard rock, as a general rule nothing need be done to preserve them, but when a fossil has been extracted from a sand it is often very brittle. It may be covered by a solution of gum, which soaks into the shell and so cements it together and helps to preserve it.

Fossils from clay frequently contain iron pyrites, a yellow, glistening mineral. If this is kept in ordinary moist air it is converted into a pale green crystalline material called iron sulphate, and during the chemical transformation the whole of the rock and fossil may be converted into a powder. In consequence, a beautiful specimen may be placed in a drawer, and in a few months may be entirely destroyed.

In order to prevent this destruction all that is necessary is to prevent the moist air from reaching the pyrites. The fossil should he dried and then dipped in molten paraffin wax, and allowed to have a layer of the solidified wax left on it or it can be covered with a thick solution of gum which, when it dries, protects the fossil from the air.

Very minute specimens can be gummed on to card­board and kept in a glass-topped box, while larger but brittle fossils can be placed on cotton-wool in a similar type of box.

For rough labelling the gummed paper attached to stamps can be used. This will stick quite firmly on to most rocks except very jagged ones and sandstones.

When arranging the specimens in a cabinet the fossils from one set of beds should be kept together. Thus if a collection has been made in the south-east of England the specimens from the Tertiary beds should come together, then those from the chalk, then those from the gault, and so on. If possible, keep those from any one bed in a drawer by themselves.

Do not mind putting a poor specimen into your collection if it is the only one of its kind you have. When you get a better one you can throw the first one away and so gradu­ally improve your collection.