重新思考傳說：野柳龜
野柳地名起源有不同的說法，傳說西班牙船員看到海岬，他們大喊這是「惡魔角」（punto diablo)， “d”與“b”的發音被省略，保留下來的音節為“ia-lo”，發音與野柳相似而得名。其他起源說法則具有更多當地居民的意義。
野柳是早期台灣人們生活的聚落之一，有些故事與傳說在世代間流傳下來，其中一個傳說將地景與想像結合在一起，說道野柳岬其實是隻烏龜精踡伏在海邊作祟，破壞航行經過的船隻，還衍生出很多其他更複雜的故事版本。
傳說是根基於事實的想像，外星人地質歷史學家Dren博士嘗試解讀「野柳龜」，他/她/祂將科學線索與知識彙整在白板上，但是他/她/祂需要有人拜訪野柳岬來驗證他/她/祂的想法，你可以接下這個任務、完成他/她/祂的工作嗎？
「野柳地層主要組成為沈積岩，軟岩層被海洋侵蝕後留下硬岩層，最後形成海灣，這是海洋侵蝕作用的結果。」Dren博士說。「地層一開始應是水平的岩層，若是你看到地層不是水平的，那表示有地質活動改變地層。」
「我認為野柳岬是單面山，所謂的單面山是一面斜坡平緩而另一面斜坡陡峭的山丘或山脊。」Dren博士解釋。「請閱讀以下跟岩石、岩層、侵蝕作用、與指標化石有關的知識，這些知識可以協助你瞭解單面山如何形成，並協助你如何探索它。地球保存了所有的改變。」
這個地質寶要做什麼？
辨識野柳的岩層，瞭解單面山的知識，與探索單面山。
水平岩層
地層是指一層在地球表面形成的沉積岩、土壤、或是火成岩，每個地層的特徵有內部一致性，可以和其他地層區分開來，正常來說，後來形成的地層會水平地分布在較早形成的地層上方，一層一層堆疊上去後形成水平的地層，野柳岩石地層從上到下分布依序為砂岩、頁岩、鈣質砂岩、砂岩、與頁岩。他們約在2000萬年前在海面下沉積而成，大約600-1000萬年前透過造山運動而抬升。
單面山
單面山是一面斜坡平緩而另一面斜坡陡峭的山丘或山脊，地質活動會抬升岩石，像是板塊相撞、斷層、褶曲，單面山緩坡表層硬度較高的岩石對侵蝕作用有較高的抵抗力，另一方面，單面山陡坡則為有地層相的斷面，軟岩層受侵蝕的速度較快，可能會形成垂直的斷崖。
野柳的岩層有不同的硬度，岩石硬度依序為鈣質砂岩、砂岩、頁岩。這些岩層受造山運動抬升高於水面，且這些岩層變得褶曲傾斜。侵蝕作用移除(單面山)兩側表面岩石，但是陡坡的軟岩層受侵蝕速度較快，上方岩層便失去支撐力而加速侵蝕作用，差異侵蝕讓陡坡變得更陡。
侵蝕作用與指標化石
一般來說，岩層會按照時間依序排列，即使地層抬升會改變岩層的方向(傾斜或倒轉)，岩層還是會彼此相連在一起，除非受到侵蝕(沈積)或是風化作用影響。
海洋侵蝕作用透過海水移除岩石，會形成海蝕洞、懸崖下切、海岸線後退、與海蝕平臺(詳見上方圖示)。風化作用則會改變岩石表層顏色或是讓岩石變得脆弱。野柳岬的岩石持續受到侵蝕作用與風化作用影響，可以觀察到多樣的地景變化。
野柳岩石中可看到海膽的化石(實體化石)和其他生物活動的化石(生痕化石)，有時一種出現在特定區域的特定化石可當作指標，顯示這區域的岩層在同一個時間形成，這是一種辨識岩層成形於相同時間的有效工具，即使這些岩層受到侵蝕作用與風化作用的影響。野柳地質公園中可發現一種實體化石，他們是野柳星楯海膽(Astriclypeus yeliuensis)與外武崙星楯海膽(Echinodiscus yeliuensis)(為一種沙錢海膽)，為兩個中新世的台灣特有種。
現在你已經知道如何辨識岩層中時間順序的知識，接下來請按照路線探索這個地質寶，最後請重新思考野柳龜傳說。
Rethink Legend: Yehliu Turtle #Cuesta
The origin of the name, Yehliu, has different legends. Legend said that Hispanic sailors saw the cape rounded with reefs and they yelled “punto diablo”. The pronunciations of “d” and “b” were excluded, and then preserved “ia-lo” which is similar to Yehliu. Other legends had more meaning of local residents.
Yehliu is one of the spots where people lived in early Taiwan. Some stories and legends were told in generations. One legend interestingly combined the landscape and imagination. It said that the cape of Yehliu is a turtle monster crouching down by the sea and boats were destroyed while shipping around. Many other stories were told and evolved into more complicated versions.
Legend is imaginations based on facts. Alien Geological historian, Doctor DREN, tried explaining the legend about “Yehliu Turtle”. They had collected scientific information and knowledge on the board. But they need someone visiting the Yehliu Cape to validate their thoughts. Can you take this task and finish their work?
“The strata of Yehliu are mainly composed of sedimentary rocks. The formation of sea bays is the result of sea erosion on softer rock layers while those hard and solid ones may therefore turn into sea capes eventually.” Dr. Dren said. “Stratum originally should be a horizontal layer of rock. If you find out that the stratum is not horizontal but a slope, it means tectonic activities changed the layer of rocks”
“I think the cape of Yehliu is a cuesta. Cuesta is a hill or ridge with a gentle slope on one side, and a steep slope on the other. ” Dr. Dren explained. “Please, read these knowledge about rocks, rock layers, erosion and index fossils. The knowledge can help you understand how the cuesta was formed and how to investigate it. All changings are preserved in Earth’s artwork.”
What to do with this earthcache?
Recognize rock layers in Yehliu. Know the knowledge of cuesta and explore it.
Horizontal Rock Layers
A stratum is a layer of sedimentary rock, or soil, or igneous rock that was formed at the Earth’s surface. Each layer of rock has internally consistent characteristics that distinguish it from the other layers. In normal strata, the later strata are laid down on earlier strata in horizontal layers. Eventually, a parallel layer was formed with a layer lying upon the other. The upper layer was younger than the layer lying under. Rock layers from top to down in Yehliu are sandstone, shale, calcium-rich sandstone, sandstone, and shale. (see picture above) They were formed with deposition under sea around 20 Ma years ago and were uplifted with the orogeny around 6 to 10Ma years ago.
Cuesta
Cuesta is a hill or ridge with a steep slope on one side and a gentle on the other. Geological activities, like plate collision, fault, folding, would uplift the rock layers. Hard rocks on the surface of the blackslope of the cuesta are more resistant to erosion. On the other hand, the frontslope of the cuesta comprised an escarpment with the strata. Soft rock layers were eroded faster than hard rock layers, probably forming into a vertical cliff.
Rock layers in Yehliu have different hardness. Top to low hardness of the rocks in sequence are calcium-rich sandstone, sandstone, then shale. The strata were uplifted by the orogeny above the sea level and these rock layers were folded with inclines. (see picture above) Erosion removed rocks on the surface of each side (cuesta). But, the soft rock layers at the frontslope were eroded fast, losing the support to upper rock layers. Differential erosion made the frontslope more steep.
Erosion and Index fossil
Generally, rock layers laid down on the other in sequence along the time changing. Even though the uplifting changed the (incline or reverse) direction of the rock layer, a rock layer will still connect with the other in sequence unless the work of erosion(deposition) or weathering.
Coastal erosion removes rocks with sea water. It would form a sea cave, downcut the cliff, retreat the coastal line, and form the wave-cut platform (see the picture above). Weathering would change the color of the rock’s surface or make rocks more vulnerable. Rocks in Yehliu cape were continuingly influenced by erosion and weathering. Diverse landscapes can be observed.
Fossils of sea urchin (body fossil) and some creature’s activities (trace fossil) can be discovered easily in Yehliu. Sometimes a kind of specific fossil only shown in a specific area can be an index for layers that were formed at the same time. It is a useful tool to recognize the exact same layer even though these rock layers were affected by erosion and weathering. Recognizable Body fossils in Yehliu Geopark are Astriclypeus yeliuensis and Echinodiscus yeliuensis (known as sand dollar sea urchin), which are two specific species of early Miocene in Taiwan.
Now, you have learned how to recognize the element of time in rock layers. Then, follow the route with waypoints to explore this earthcache. At the end, rethink the legend of Yehliu Turtle.
Logging Task
Rock layers and Fossil
1.1 Visit spot A, B, and C. What’s the main type of rock layer in each spot? Do you find fossils in each spot?
1.2 How many different layers do you find in spot C? Which layer is abundant with fossils?
Cuesta
2. Spot A, B, C and the posted coordination are in different heights. Are you walking on the frontslope or backslope? Do you walk on the top of the same layer? Explain your answer.
3. Take a look at the posted coordination. Do you discover the cuesta? Can you observe the strata at the frontslope? Describe your observation on counting strata. Or explain why it is not clear in different layers.
4. Predict the change of the cuesta at the posted coordination. Will it collapse? Or will it remain? Explain your prediction.
5. Rethink Legend: Is there any geological evidence at the posted coordination for the legend telling that “the crouching turtle destroyed the boats and ships”?
6. Rethink the legend: Find the turtle in the legend. Photo “it” with you, your identifying item, or your GPS device.
Log this cache "Found it" and send me your suggested answers either via my profile, or via geocaching.com (Message Center) messaging, and I will contact you if there is a problem. Don't post answers in the log except logging task 6, please.
登錄任務
岩層與化石
1.1 探訪A、B、C三個地點，各個地點的岩層中主要岩石為何？各個地點有找到化石嗎？
1.2 在地點C可以找到幾個不同的岩層？哪個岩層有豐富的化石？
單面山
2. A、B、C三個地點與地質寶點分別位在不同的高度，請問你走在陡坡還是緩坡？請問你是否走在同一個岩層的上方呢？
3. 在地質寶點觀察，你有發現單面山嗎？在陡坡處能否觀察到地層相？描述你看到多少個地層，或是解釋為什麼地層相並不明顯。
4.在地質寶點預測單面山的變化，會崩塌嗎？還是會維持原樣？解釋你的預測。
5. 重新思考傳說，站在地質寶點觀察，烏龜作祟破壞船隻的說法是否有地質線索來解釋呢？
6. 重新思考傳說，找到傳說中的烏龜。請和他拍照，相片內容包含他和你、你的代表物、或你的GPS裝置。
線上登錄這個地質寶，請寄到Geocaching.com的信箱，若有什麼問題，會再回覆給你。除了登錄任務6，請不要在線上log中公佈你的答案，感謝。
Reference
Cuesta @wiki
野柳地質公園
北海岸野柳風景區之地形地質與自然 數位典藏(一)
$$ 野柳地質公園有入場費用 $$ Entrance fee to this Yehliu Geological Park
大眾交通工具 Public transportation
Bus 1815 from Taipei Main Station to Yehliu
台灣好行 716 皇冠北海岸線 Crown Northern Coast Shuttle Bus from Dansui to Yehliu