AY Honors/Fossils/Answer Key
Collecting fossils for yourself can be a very relaxing and often rewarding hobby. There are no special rules about where one may find fossils, and you can find fossils in many places where sedimentary rocks are exposed, such as clays, shales, limestones, and sandstones. Only certain sedimentary rocks will yield fossils, and they are often concentrated along particular bedding planes within the rocks.
Finding fossils
Fossils are not to be found in areas of igneous rock (except in some beds between lava flows). In rocks which have undergoone metamorphism, they are usually so distorted that they are difficult to recognize or have been destroyed completely.
Establishing the age and type of the rocks in your area with the aid of a geological map (usually available from your local state or national geological survey) will provide you with an idea as to what types of fossils to expect. Most libraries should have local geological guide books, but, a word of caution: they may be out-of-date. Many hours have often been spent trying to locate a quarry that has since been filled in.
There are a large number of well known fossil collecting localities worldwide, and at some of these classic localities fossils have been recovered for a long time. Many such sites are recorded in geological guide books and other sources of literature. At such localities fossils are almost sure to be found, but one should remember that generations of fossil collectors have collected there before.
A visit to your local museum is often useful too. However, one should take into account that many of the inspiring specimens in museum collections may have been collected a long time ago, often when the site was in prime condition.
You may also consider joining a rock and mineral club or natural history society. Up-to-date information from other collectors is usually the best, and often such clubs and societies have access to private collecting sites that would not otherwise be accessible. Supervised parties are usually allowed to collect fossils in quarries, whereas individuals may be discouraged from doing so. The staff at operating quarries will often know where the best spots for collecting fossils are.
Artificial exposures, such as road cuttings or quarries, can often be good collecting spots, along with continually eroding river or coastal exposures. Coal mining operations often yield excellent fossil plants, but the best ones are to be found not in the coal itself but in the associated sedimentary rock deposits called coal measures.
In hilly regions the best sections are often those exposed at the sides of streams that have cut into the bedrock.
Wave washed sea cliffs and foreshore exposures are often good places to search for fossils, but always be aware of the state of the tides in the area. Never take chances by climbing high cliffs of crumbling rock.
Exposures of softer rocks, such as clays and sands, can be good collecting spots. However inland sections tend to degrade rapidly, becoming overgrown, and are lost forever.
Collecting ethics
Wherever you decide to collect fossils you should always seek permission from the land owner or authorities first. Thoughtless or unreasonable behavior on the part of one collector may mean that access to a particular site in the future is refused to others. Irresponsible behavior while out collecting may also put yourself and others at risk.
Hammering the rocks in national parks and other areas of natural beauty is often discouraged and in most cases is illegal, so please be considerate. In this way fossils will still be there for future generations to appreciate.
Field collecting
Do not hammer at rock outcrops aimlessly, and never leave rock fragments scattered over fields or roads. The irresponsible destruction of an outcrop in search of one or two fossils is not welcomed. Fossils should be collected sparingly, and preferably without the use of a hammer.
Often the best fossils are those which have been weathered out of the rock over a long period of time. They may be visible on the surface of the rock, or among the loose scree at the foot of an outcrop. Searching for fossils on the ground is largely a matter of patience and a keen eye.
It is always better to leave a fossil in the field rather than try to dig it out in a hurry using the wrong tools, you could damage or destroy a valuable scientific find. Collecting is often a matter of personal judgment; consider the scientific value of the fossil and whether it would otherwise be damaged or destroyed by erosion. Would it be better to collect the specimen now, or return at a later time with the appropriate tools? If you think that the removal of the specimen is essential, then do it. Otherwise, contact an authority at a local university or club that can help you.
Equipment
It is important to have the right kind of field equipment when looking for fossils, and safety should always be your primary concern.
A hard hat is essential to protect you from loose stones which may be dislodged from cliffs above, but remember that this will not protect you from larger falling rocks. Hard hats are normally a requirement in operating quarries.
Safety goggles and protective gloves are also essential. Rocks can be sharp and dangerous, safety goggles will protect your eyes from chips while hammering, and gloves will protect your hands.
You should always dress appropriately for collecting trips, taking into account the climate and terrain of the area. Sturdy footwear, such as walking or hiking boots, are usually a must. In general, wear old clothes because you will almost certainly get dirty. A hand-lens is also important as it will enable you to recognize fine details in both the rocks and fossils they contain.
A hammer, chisel and wrapping materials are the basic equipment required for fossil collecting, along with a stout rucksack or canvas bag for carrying your equipment and your fossil finds.
Remember that the steel of many ordinary hammers are too soft for use on most type of rock. The steel may splinter and the flying fragments may cause injury, not only to the person using the hammer, but to his or her companions as well. Always strike with the hammer away from the body.
Use a good quality geological hammer or rock pick, such as those manufactured by the Estwing Manufacturing Co, Inc. of Rockford, Illinois, USA, which is a carefully designed tool and is useful for most types of rock.
The head of a geological hammer or rock pick is made from specially hardened steel designed for use on rocks. The head is either firmly attached to a wooden shaft, or the hammer may be of the type where the head and the shaft are cast from one piece of steel. The head has a square face at one end, while the other end either tapers to a point of has a straight chisel edge. The point of such picks are not meant for striking rock directly, but for tapping rock (such as shale) open along planes and for prying. The hammer end is meant for striking.
In dry climates shrinkage can be a problem with hammers which have a wooden shaft, the wood may shrink so that the head becomes loose.
A convenient weight for a general purpose geological hammer or rock pick is around 1 kg (2 to 3 pounds). For breaking very hard rocks one may need a hammer of between 3 and 6.5 kg (7 and 14 pounds) in weight, with a correspondingly longer and thicker shaft.
For extracting fossils from harder rocks, a sturdy mallet and cold steel chisels may also be required. Usually one needs a range of chisels in size from small ones with a sharp edge of about 1 cm (quarter of an inch), to much larger and heavier chisels. A broad-bladed chisel is often very useful for splitting rocks along their bedding plane.
Knowing the type of rocks on which one will be working is useful so that one can select the appropriate tools and not have to carry any unnecessary weight.
Different types of rocks will break differently and a beginner should put in a little practice, getting the feel for a particular type of rock before he or she starts hammering out fossils. It is all too easy to ruin a specimen with one ill-placed blow of a hammer.
Extracting a specimen that is embedded in solid rock may prove to be a long and difficult process. Before attempting to extract a specimen, the collector should make sure that it is feasible to remove it without destroying or damaging it. Be sure to leave sufficient rock beneath the specimen to protect it from fracturing; excess matrix can always be trimmed once you get the specimen home.
For soft sediments and unconsolidated deposits, such as sands, silts and clays, a spade and a flat-bladed trowel or stout bladed knife may be the most useful tools for clearing the area around a fossil. Brushes are also useful for removing loose sediment from around fossils. Also, a word of caution: whenever grinding or chipping rock beware that the rock dust created can be very harmful to the lungs. Always take appropriate measures, such as using a mask or respirator, when doing anything with rocks that create dust.
Use a sieve to separate fossils from sands and gravels. Usually a smaller mesh is required in order to avoid losing small fossils. One practical difficulty with using sieves in the field is that they easily become clogged, especially when the material sieved has a high moisture content. However, under dry weather conditions the more durable fossils, such as teeth and bones, can be quickly and easily sieved out of loose sands. Remember that shaking the sieve is always liable to damage or destroy fragile fossils.
If there is water available, such as on a beach or next to a stream, the material containing the fossils can be sieved wet and the matrix gradually washed away. Wet sieving is a technique that is frequently used for the collection of small mammalian fossils, and by using this technique even the smallest specimens may be recovered. Any fossils you will thus obtain create a more balanced representation of the fossils present at that particular locality. Alternatively a block of matrix with the fossils inside may be dug out and taken home for treatment indoors. To do this use a flat-bladed trowel, or stout bladed knife, and simply carve away the surrounding sediment. Once free, carefully wrap the matrix block containing the specimen before taking it home.
Before setting out on an expedition, ask other collectors who are familiar with the area where you intend to collect exactly what tools are needed.
Preservation and documentation
Always record field notes, such as the locality, types of rock, and fossils seen in a sturdy notebook using waterproof ink. A long tape measure is useful to record the levels of the beds in which you find fossils, and a camera may also be useful for taking photographs of fossils in situ. Detailed field notes are an essential part of your records, both from the point of view of keeping an accurate account of your collecting activities, and as an indispensable aid in the subsequent identification of your finds. Your field notes may in time be the only reference to a collecting area that later becomes destroyed by erosion or by the spread of urban areas. If often helps to make sketches of the site, particularly if the fossils are found in certain distinct bands or horizons within the rocks. Accurate notes will enable you to readily identify such horizons on your return trips.
Having collected fossils it is essential that they are adequately protected from damage while they are being transported home. Each fossil or piece of rock containing a fossil should be carefully wrapped. Here newspaper, paper towels, sticky tape, polythene bags and an assortment of small boxes or tins will all prove to be useful.
The more fragile specimens will need the greatest protection, such as packing them in a tin or box lined with a soft material such as cotton or wool.
All specimens collected should be labeled in the field with the details of the locality where they were found. The easiest and safest way to do this is to write the details in your field notebook along with a number for each specimen, a corresponding number can then be written on the wrapping used for each specimen or on a ticket or scrap of paper included with the wrapping.
If you do not label the specimens as they are collected and wrapped there is a distinct danger that errors will be made in the localities from which the fossils were collected, especially if they are not unpacked for some time after they were collected. The value of any fossil that does not have accurate locality details is greatly reduced.
Maps and a compass/clinometer or GPS receiver will assist you in finding fossil locations and assist you in recording your field notes.
Occasionally, large fragile specimens may need to be surrounded and supported using a jacket of plaster before their removal from the rock. This will protect the fossil and prevent it from shattering. In this case clean the fossil and expose as much of it as possible. Then cover the exposed surface with a separator (wet paper of plastic film is suitable), followed by layers of plaster bandage. Once the plaster has hardened you can lift the fossil out of the surrounding rock, and then repeat the plastering process on the underside of the specimen.
