A Beach Walk in New Mexico
I was in sixth grade when I first found proof of a sea existing over New Mexico. I was planting strawberries in the backyard when I found a seashell. It wasn‘t an ordinary seashell like the shells my sisters use in the sandbox: it was fossilized. It was small and gray and as hard as a rock, and yet it was the exact shape and size of a seashell. I was intrigued by the idea of small clam-like creatures living in my area, but never ventured to explore this more. But two years after finding that shell, I asked myself: was the seashell in my backyard discarded by a former resident, or could I find other, similar seashells near my home? My parents told me about a hike west of Church Rock, New Mexico, where they had found fossilized seashells. They agreed to take me and on May 28, 2001, we left for the seashore.
White Cliffs Trail, an eight-mile loop, begins two miles northwest of Pyramid Rock, a local landmark. The trail follows the course of a mesa and hogback that enclose Cliff Dweller Canyon, named for its Anasazi petroglyphs (Figures 1a and 1b). Both White Cliffs and Cliff Dweller canyon are used today for grazing sheep and cattle. The elevation of the eight-mile loop ranges from 6,800 to 7,400 feet above sea level (Tempest, p. 18).
May 28 was bright and warm, with many flowers blooming. I took many photographs of flowers and other things that caught my eye. Near the trailhead, I saw several cliff swallows and stopped to watch them. I tried to photograph one, but he was much too fast for me. I also saw a coyote dash across the trail.
Journal Entry: May 28, 2001
Today I went to New Mexico‘s seashore. I wanted to collect some seashells and see the work of millions of years. It took two hours to hike to the shore, as I allowed time for distractions such as insects, flowers, and odd-looking rocks.
The first thing my parents and I noticed was a clicking sound. The sound surrounded us and we thought it was insects. We walked a little ways, only glancing at the ground and bushes for the insect, but soon decided to look into a tree. On each branch we saw a cicada, moving its wings to create a small sound. I never knew small insects, even very many in chorus, could make such a loud noise together.
We paused several times to examine and take photos of bright wildflowers. As we walked, the sun grew higher in the sky and the flowers opened up wider and wider. The flowers that we had thought looked beautiful at 8:30 am looked even more so at 10. The cacti had big pink flowers that brightened up the ground. The blossoms on each yucca plant were very pretty. Each stalk of petals seemed to be taller and to have brighter colors than the last (Figure 2).
On the cliffs, each rock layer was a different color. In one place, a rock stuck out like a peninsula on a continent. But what interested me was not its shape but its coloring. On the main part of the cliff, the rock was mostly red, with a little bit of white. But on the "peninsula" there was a lot of white rock. I had never seen this combination of red and white rock before.
After two hours, we came to the seashore. It started off as a few large chunks of what appeared to be cement. But upon closer examination, I realized it was really a lot of fossilized seashells cemented together by earth. There were also some loose seashells and many small pieces of shells that had been cracked (Figures 3-4).
As we walked, we noticed seashells mixed in with the soil below our feet. Many people must walk and bike here and never notice the fossils. They are fixed on their destination, and don‘t bother to think that there could be fossils under their feet.
After some more walking, we arrived at our destination, the main deposit of seashells. Around us were huge boulders made entirely of shells. Although the shells did not maintain their colors and sparkle, the boulders were very pretty. Wind and rain had arranged the shells in patterns that gave the soil and boulders a shine.
Lying among the shells were pieces of calcite. Once again, I thought of man-made things as I had when I first saw the seashells in rock. The calcite looked like smooth glass. But the calcite was thick and had different colors in it. It did not feel as smooth as glass usually does. One side of the calcite was rough and looked like an ordinary rock, but the other side was bright and shone like water.
I also stopped a moment to look at an area where a lot of salt had collected. From a distance, the salt looked as if it were on top of regular soil. But when I stepped on it, I realized that it was a thin crust lying on top of mud.
One large rock reminded me of an Egyptian sphinx. It was large and rectangular but had a "head" coming out of one side (Figure 5).
At home, my reading confirmed that the shells I saw are from the Cretaceous period, 70-135 million years ago. During the Cretaceous period, all of Europe and half of North America were submerged in water. The North American seaway ran from the equator to the Arctic and was about 800 meters deep. Most geologists also believe that North America was attached to Europe during this era (Lambert). The shells I saw are clam-like shells that could be "pelecypods" (Ratkevich).
The pelecypods probably fed off of blue-green bacteria or blue-green algae. Although the seaway, like the pelecypod, is long gone, blue-green algae survive today, alongside the White Cliffs trail, in cryptobiotic soil. Cryptobiotic soil forms where blue-green algae bind sand grains together. This keeps soil in place and prevents erosion. Cryptobiotic soil also helps to attract potassium and calcium, minerals fostering plant growth. Cryptobiotic soil, then, is very important in a desert ecosystem. I have heard that it can take cryptobiotic soil anywhere from 50 to 250 years to recover from one footstep. I will certainly avoid walking on any when I go off-trail.
I looked for fossil cephalopods on White Cliffs trail, but I have found these spiral fossils only at a road cut in McGaffey National Forest, about 20 miles southeast of White Cliffs (Figures 6-8).
Approaching the White Cliffs on June 24, 2001, I could see both Pyramid Rock and Church Rock (Figure 9). A close look at Pyramid Rock revealed several layers of rock. Since new layers of rock build on top of old layers, younger layers usually top older layers. However, faults and weathering rearrange and wear away rock, and some rocks, such as sandstone and limestone, are more resistant than shale and mudstone. At Pyramid Rock, Orange Wingate Sandstone (Figure 10) represents the remains of a vast Sahara-like desert, formed during the late Triassic or early Jurassic era (geologists are not agreed on the exact era). The next layer is Jurassic Entrada sandstone. The last two layers are from the Cretaceous period, Morrison Sandstone and Dakota Sandstone (Rigby, Baars 1995). The shells I found are from the Dakota Sandstone layer.
Before reaching White Cliffs, we saw to the east the ruins of an old coal mining operation. Coal forms when plants die in wet, acid conditions. Instead of completely rotting, the plants turn into soft, fibrous peat. Overlying sediments drive out the moisture and squash the peat, making it lignite, or soft brown coal. Greater pressure creates bituminous coal, which is harder, blacker, and has an even-higher carbon content. The coal‘s final stage is anthracite. This coal is hard, black and shiny, and has a higher carbon content then any other stage of coal. Coal is rich in carbon because it is made of plants. Most coals are remains of low-lying forests drowned by invading seas and buried under sediments. Coal in our area is Cretaceous in origin (Lambert).
Surrounding the White Cliffs are hogbacks, formed by steep, even-crested ridges. Hogbacks, common to the southern Rockies, form when the layers of rock dip sharply. They have steep slopes and a bed of resistant rock. But surrounding the resistant rock is a bed of easily eroded rock (Lambert).
Journal Entry: June 24, 2001
Today I returned to the seashore. I hoped to observe the plants and wildlife near the shells, as well as to find and photograph some new and more unique fossils.This time the flowers had all wilted and dried up. Only a few yuccas had blossoms. The flowers were wilted and their stems broken. We saw yucca fruit that had fallen off the plant. The cacti were bare. Cacti are harder to notice without their blossoms.
This time we were not greeted by chirping cicadas. Instead, we saw their skins. There were many skins on the ground, as well as skins attached to bushes and trees (Figure 11). We even saw several yuccas that had cicadas attached to them.We noticed some shells earlier than we had last month. We must have thought that they were just ordinary rocks mixed in the dirt, but this time we noticed right away that they were shells. But we didn‘t find any interesting fossils until we came to the main deposit. We found two interesting fossils.
One was an imprint of a small ruffled shell; the other was an imprint of a leaf (Figures 12-13). I had not found any other fossils like them before. From my reading, I think that the fossils are from the Cretaceous period, about 70-135 million years ago. During this time much of Europe and about half of America were submerged in water. It is hard to imagine so much of the world covered in water.
On June 24, I was surprised at how dry it was. But it was dry because there was no rain or melting snow to feed the plants. In May, melting snow fed the flowers that bloomed alongside the trail. By June the snow was gone, but the summer monsoons had not yet begun.
Throughout the Cretaceous era, ferns and coniferous trees grew here. But at the close of the Cretaceous era, an important phenomenon occurred: plants flowered. This was a new development (Fortey). I found the leaf imprint in a gully where it had washed down. This fossil is probably from the topmost layer of the Dakota Sandstone and washed down with melting snow.
The development of flowering plants during the latter part of the Cretaceous era is significant because it happened as other life forms reached extinction. According to one geologist: "The meteoritic dust cloud that supposedly killed off the dinosaur‘s food supply was not as affective sic as postulated. The grasses and flowering plants that first appeared in the Cretaceous time flourished into the Tertiary period!" (Baars 2000, 174).
Journal Entry: October 8, 2001
Today we walked on White Cliff Road to visit the gully with the fossils. It was sunny but not too hot. I
The rabbit brush and sage are still growing although the rabbit brush will seed soon. Long after the other plants and flowers have stopped blooming, you can see the rabbit brush‘s bright yellow blossoms. This way, the rabbit brush does not have to compete with its more colorful rivals to be pollinated (Figure 14). The sage seemed more noticeable today; perhaps that is because there are not as many other flowers to see.
We saw four tarantulas on our hike. They were about two inches across from one extended leg to the other. We provoked one of the spiders and it grew stiff and threatened us by lifting and waving two of its long legs (Figure 15). We also saw a wasp that I later found out to be a Pepsis wasp (Pepsis chrysothemis), commonly known as a tarantula hawk. It was about one inch long and had a black body. Its wings were bright orange. This wasp lays its eggs on the abdomen of a tarantula. First, it stings the tarantula to paralyze it. Next, the wasp drags the tarantula to a hole in where she lays an egg on the tarantula‘s abdomen. The wasp then leaves the hole and covers it up. When the new egg is hatched, the wasp larva eats the paralyzed and comatose tarantula (Arnett, Tweit).
Although some flowers are gone, we saw two Indian paintbrush plants. Indian paintbrushes have red leaves and green flowers that stick out at the top. However, the red leaves resemble a flower (Figure 16).This time we went down into the gully to look for fossils. In the gully we saw a section of wet rock that indicated an underground spring. We also saw a large prickly pear cactus. We did not find any new types of fossilized seashells, although we did see thousands of the types of fossils we had found previously.
We went a little further up the trail, past the main deposit of shells. A little way off the trail we found an overlook. We walked around, looking down into faults and cracks in the rock. But we stayed away from their edges because they were 18 inches wide and about 20 feet deep. In some places we found aquifers that held water from a rainfall earlier this morning. On this overlook my dad saw some indentations resembling hand- and footholds. Perhaps these were Anasazi footholds leading to aquifers.
Later, walking back, I found an old pottery shard. I was surprised because we had walked on the same road earlier that day but not seen anything. Maybe this pottery shard was uncovered by a pickup on the road. I took a picture of the shard, then covered it with pine needles for someone else to find (Figure 17).
As I examine fossils of extinct clams, I try to imagine the feel of the humid, salty air and the flash of swift-moving predators. This thought brings to mind Attending Marvels, in which scientist George Gaylord Simpson writes: "Fossil hunting is far the most fascinating of all sports... The fossil hunter does not kill; he resurrects. And the result of his sport is to add to the sum of human pleasure and to the treasures of human knowledge." I set out to explore the White Cliffs for fossilized seashells; in the process, I also observed animals and flora of present-day New Mexico, and their interrelationships. I was reminded that fossils are not just shells, but evidence of a past ecosystem that has evolved into our present ecosystem. As to the fossil shell that I found in my backyard, it is a remnant of the vast Cretaceous Ocean that once swept over New Mexico.
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Copyright © 2002 American Museum of Natural History
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Supplement a study of geology with an activity drawn from this winning student essay.
- Send students to this online article, or print copies of the essay for them to read.
- Have them research your area's geologic history and whether any fossilized seashells have been found, reporting on what they learn.
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