Colourful bluffs in Long Island recall the most recent ice age

Deborah Painter (USA) Imagine a tremendous piece of land moving equipment that scraped up the soil and some of the surface bedrock from four states within the United States’ Eastern Seaboard, carrying and dragging it all the way, before dumping it on a ridge off the shoreline. That is what essentially occurred with the final advance of the Wisconsinian ice sheet, the only one which left glacial deposits visible in New York State today. Long Island is a ridge of Cretaceous bedrock with glacial deposition. The moraines there have not been ground into sandbars and spits along the western end of the north shore as much as elsewhere, because of the sheltered nature of the Long Island Sound. Therefore, shoreline bluffs expose rocks as well as glacial loess. Fig. 1. Fishermen’s Drive takes you to the loess deposits. To park at the beach requires a permit. (Photo by JB Steadman.) If you find that your journeys take you to New York City, one of the world’s largest metropolitan areas, try to make time to visit Caumsett State Park at Long Island Sound. My own visit began when planning a visit to New York State’s Long Island to see my friend, Joyce Raber. She suggested various things that we might do: go to a Broadway play, go shopping and so forth. However, my list of things to do was typically “eco-tourist”. I wanted to visit the famed American Museum of Natural History in Manhattan, then see nearby Central Park, where the … Read More

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Jamaica’s geodiversity (Part 1): Introduction and some older highlights (Cretaceous to Miocene)

Stephen K Donovan (The Netherlands) and Trevor A Jackson (Trinidad) With a length of only about 240km, Jamaica cannot be considered a large island. It is also relatively ‘young’ geologically, the oldest rocks being only about 140myrs old. This might sound old enough, but contrast it with, for example, rocks in the islands of the Scottish Outer Hebrides, which are about 2,000myrs old. But Jamaica is nevertheless noteworthy in having a rich diversity of rock types and geological features, and it is rightly known for its high biodiversity, both on land and in the surrounding seas. To give one example, the 500 or more species of extant land snails make Jamaica a biodiversity ‘hot spot’ for these familiar molluscs. However, Jamaica should similarly be recognised as a geodiversity hot spot, with a range of geological and physiographic features, strata and fossils that make it an unusually fruitful focus for earth sciences research. We could support our bold assertion by a detailed exposition with tabulation of principal features and comparison with similar-sized islands elsewhere, although such an approach would perhaps be better suited to a dry research journal. The potential for producing such a long, boring discursion is large and we intend to avoid the temptation to do so. Rather, we want to illustrate Jamaica’s geodiversity by reference to a dozen key features. These are available for inspection to anyone who is interested and which we will describe in two articles in Deposits. The choice of these features is personal – … Read More

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Geology of islands

 Stephen K Donovan (The Netherlands) Islands are attractive places to visit, not just for geologists. Nonetheless, for us, they provide three advantages that favour collecting and research in the Earth Sciences. One of the attractions of an island is its small size in comparison with continents. The corollary of this small size is its relatively long coastline. Assuming that our island is not the mound of sand with a palm tree so loved by cartoonists, a long coastline indicates abundant exposures of rock, commonly well-exposed and accessible. Second, because of their relatively small size, islands offer a limited possible area of outcrop. The island may be volcanic in origin, so you may have one (or a few) volcanoes and its deposits to map, log and sample, producing a self-contained study. A particular sedimentary deposit may be (probably will be) limited to a single island. If you want to determine the palaeontology or palaeoenvironments of this deposit, the only place it can be studied is on one island. To give one example (among many), the Middle Miocene Grand Bay Formation, exposed on the east coast of Carriacou in the Grenadines, Lesser Antilles, includes the only crinoid-rich deposits in the Caribbean Islands. I had been studying the few Antillean fossil crinoids for ten years until I went to Carriacou and the sum total of specimens I had collected until then could have rested, comfortably, in the palm of one hand. From Carriacou, I collected bags of crinoid-rich bulk sediment samples (Donovan and … Read More

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Rose and blue quartz

Steven Wade Veatch (USA) Quartz (SiO2) is a common mineral found in all three classes of rocks (igneous, metamorphic and sedimentary), in many environments and in a range of colours. However, rose and blue quartz are less common than some of the other varieties. This article discussed these two extraordinary minerals. Rose quartz Rose quartz has a pale pink to rose-red colour, thought to be caused by trace amounts of titanium, which absorbs all colours except pink. In a laboratory experiment, samples of rose quartz from several localities were carefully dissolved in acid. The remaining insoluble residue consisted of thin microscopic fibres, which may also be responsible for the colour of rose quartz. Well-formed rose quartz crystals are rarely found in nature, but when they are, they are generally found in massive chunks associated with pegmatites (Fig. 1). Fig. 1. This large rose quartz specimen was found at the Devil’s Hole Mine (owned by Tezaks), about a mile from the town of Cotopaxi, Colorado. (Photo © 2007 A Schaak.) The term pegmatite refers to exceptionally coarse-grained crystalline granite. Since rose quartz is cloudy, it is not popular as a faceted gem, but it is commonly made into cabochons (Fig. 2), rounded into beads for necklaces or carved into various objects. Fig, 2. A cabochon pendant from the same rose quartz near Cotopaxi. (Photo © 2007 A Schaak.) It has been named as South Dakota’s official state mineral. Here, rock hounds have a good chance of finding specimens ranging from shades … Read More

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