Discovering Delaware Water Gap:
A Field Book for Young Naturalists
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Despite all that an eagle's eyes can see, however, much more is known only to the humans. For unlike a bald eagle they can go back in their imaginations into geologic time, when warm seas, awesome mountain ranges, and icy glaciers arrived and departed from this land. Only they can learn about the Lenape Indians who hunted bear and moose here 10,000 years ago. Only they can investigate the grass, ferns, trees, and waters, and discover the birds, mammals, and fish that an eagle would miss.

What is the Delaware Water Gap?

What happened in this place long ago to create this landscape of rivers, hills, and valleys? Clues to the answer lie everywhere around us. By carefully exploring the land, geologists have put together a startling explanation.

The Delaware River makes an S-curve through the Gap.

Think big! Try to picture this: two separate Appalachian mountain ranges have appeared and disappeared in ages past. Snowy peaks of the first mountains reached their highest elevations during a geologic time called the Ordovician Period. That was between 500 and 425 million years ago (see the Geologic Time Line). These mountains were the first Appalachians, and like mountains everywhere they began eroding away into gravel and sand and mud. Rain, wind, and frost slowly wore the peaks down, leaving us today only their "roots," the deep interior of the old mountains. (You can see rocks of these old Ordovician mountains in the slate quarries near Slateford Farm and along the Interpretive Trail near Arrow Island Overlook. The slate was once sold for school slates, chalkboards, and roofing shingles.)

Near the mountains lay a large, warm sea basin, into which rivers washed the eroded gravel and sand and mud. Beneath the water this rock material, or sediment, slowly hardened into layers of sedimentary rock. Gravel turned into conglomerate; sand became sandstone; mud formed mudstone. And beneath the salty waves sea creatures lived and died just as they do in the sea today. Their lifeless shells fell to the seabottom to become fossils accumulating into layers of yet another sedimentary rock, called limestone.

Kittatiny or Kittatinny?
Over the years there have been various spellings of the name of this mountain ridge. Although we have used a single "n" in this booklet, the accepted spelling today is Kittatinny. (click on image for a PDF version)

These rock layers were deposited in the sea during the Silurian and Devonian Periods, between 425 and 350 million years ago. Except along Kittatiny Mountain and in the water gap, in all parts of the national recreation area you can find fossils in the rocks. A very common fossil is the brachiopod, a creature that had two shells but was neither clam nor mussel nor oyster. Snails lived here also. Reefs were built up from the limy skeletons of corals. Crinoids, primitive animals resembling upside-down starfish, lived on a stalk attached to the sea bottom. For a time giant eurypterids ("sea scorpions") patrolled the waters, keeping company with nautiloids, which were like octopuses in straight or coiled shells. Trilobites scurried over the sea bottom, and primitive armored fishes darted among the corals and crinoid stalks.


(Use Your Senses) This book let is a guide to exploring the environment of Delaware Water Gap National Recreation Area. Use it together with your senses and your imagination to discover the many exciting and beautiful features of this place. Your senses especially can link you to nature.

Look down into the Water Gap from high above on Mt. Tammany. Listen for ten whole minutes to the sound of a rushing waterfall. Watch a wild animal closely: how does it move, where is it going, how does it protect itself?

With your eyes closed, get a friend to lead you to a large tree. Touch its bark; can you identify it? By touch alone you can easily distinguish a shagbark hickory from a white oak or an American beech from a white pine. Walk barefooted on soft moss and pine needles. Resting on a damp stone or log, feel the cool stream water as it rushes through your fingers. Listen to bird-songs and learn to identify the singers, like an Indian, just by their sounds. Taste a pine needle. Taste the leaf of sorrel and add a bit to your salad.

Your nose can link you to nature. Scrape the bark of a spicebush twig with your fingernail, or crush a sassafras leaf; then sniff. Try smelling the blossoms of many different wildflowers and shrubs. Do the most colorful flowers have the most distinctive scents? What gives the pungent smell to a handful of forest soil? Does this tell you about its origin?

After the seas had collected vast layers of rocks and fossils, the second Appalachian mountain range began to form from them. Slowly the rock layers rose up out of the sea to become the folded Appalachian Mountains. By the Permian Period, about 230 million years ago, these new Appalachian Mountains were reaching their greatest heights, probably well over 3,000 meters high and comparable to today's Alps and Rocky Mountains. The layers of Silurian and Devonian rocks within them were being folded, bent, twisted, and crumpled. The seawater was pushed back, and on the fresh new land dinosaurs began foraging among the ferns, cycads (primitive, seed-bearing, non-flowering plants with large fernlike leaves), and conifers. All this required millions of years; folded mountains do not just explode from the earth.

Fossils in the rocks of Delaware Water Gap are clues to the life of 400,000,000 years ago.

Today we find no dinosaur fossils here. Why is this so? And what happened to those 3,000-meter peaks? You guessed it! Like the first Appalachian Mountain range, these new Appalachians have largely been worn away, including all traces of the dinosaurs that lived here. Today we see only ridges and valleys in the place of high mountains. The process of erosion has not stopped; every muddy stream that you see continues to carry away bits of the land.


(Look For Fossils) Ride or walk through the Delaware Water Gap, keeping a sharp lookout for bent or folded rock layers. From Point of Gap Overlook you can see the Silurian rocks (Shawangunk formation) that were lifted up during mountain building. Have you ever tried to bend a rock? If not, try it—can you imagine how much energy the earth must have if it actually bends rocks? Look for fossils everywhere you explore. But do not collect them, unless you have a permit! Try to identify what you find. Can you explain how fossils were preserved here? Where would you expect similar fossils to be forming in the world today?

Typical brachiopod fossils (top) and trilobite fossils.

You may wonder, when you visit the water gap, how the Delaware River managed to find or cut its way through Kittatiny Mountain, which is made up of very hard rock. The explanation is that the river was here before the mountain. Like the other mountains you see in this region, Kittatiny Mountain was formed by folding of the earth's crust. This folding occurred so slowly that the river was able to cut down through the rock layers faster than the folds were created across its path. The rock layers through which it cut are clearly visible in the gap, and there are several points at which the folding of the rocks is vividly displayed.

After the gap had been cut, there occurred an amazing event, the most recent major episode in earth's geologic history—Continental Glaciation. During the Ice Age, which spanned the last million years or so, the climate turned colder. Vast, thick ice sheets, or glaciers, accumulated from compacted winter snows. Under their own tremendous weight these sheets of ice spread slowly southward from the region of Hudson's Bay, killing everything that stood in their paths and grinding across the rocky hills beneath them. Advancing perhaps a few meters a day, the ice filled the valleys and overrode the heights. The scene was much like what you would see today on Greenland and the Antarctic subcontinent.


(Examine Glacial Rocks) Away from the river, find a road bank or hillside full of rounded pebbles or stones; the region near Peters Valley, N.J., is good. These are glacial rocks, in hills deposited by the retreating ice sheet. The fact that they are rounded indicates that they were water-transported. Sort your stones into several piles. How many kinds do you find? (Breaking the smoothed stones open with a geologic hammer helps to determine the types.) A wide assortment of stones is characteristic of these glacial deposits, for the moving ice brought "foreign" rock materials from the north. If the deposit is layered, notice the clay and sand layers. Each layer, whether stones, sand, or clay, was deposited by a stream of icewater. Do the sizes of rock particles in the different layers tell you something about the varying force of the moving water that deposited them?

Then the climate slowly warmed again. The ice sheets began to melt. Trees and animals returned as the soil emerged into sunlight. Indians came and made this their homeland. About 11,000 years ago the ice had entirely melted away. Left behind were many signs of its visit: scratched and polished rock surfaces (you can see these commonly on Kittatiny Mountain trails); hills of stones and sand (called drumlins and kame terraces); and millions of pasture stones (called glacial erratics), which you can see where farmers have used them to build stone walls.

Evidence of the passing of the ice sheet is seen in grooved and polished bedrock.

Today, the Delaware River is a broad path of quiet water. Islands such as Shawnee, Poxono, and Minisink dot the river. They are made of material that the river is too weak to wash down stream except during floods. And from the surrounding slopes, dozens of streams rush down to meet the river. These tributary streams are fast, turbulent, and full of spectacular waterfalls. This pattern of fast and slow streams in the national recreation area is typical of the Appalachian Mountains.

The life community of the quiet river is much different from that in the turbulent tributary streams.

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Last Updated: 30-Apr-2010