Stratification in volcanic rocks differs in some respects from that in sedimentary rocks. These are cross-bedding, which is common in fluvial or eolian deposits, and graded bedding, which reflects transport by density (or turbidity) currents or, in certain cases, varved deposits. Two important and distinctive structural types are recognized as characteristic of particular environments. In general, it is best developed in fine-grained sediments and is least apparent and least persistent in coarse-grained materials such as conglomerates. Stratification in sedimentary rocks varies greatly both in degree of prominence and in details of structure. Where layers have been deformed, the record of past movements of the Earth’s surface is preserved in the stratification, making possible the interpretation of geologic events and permitting such practical results as the location of mineral deposits, petroleum fields, and groundwater reservoirs. Differences in sediment composition resulting from different sources, and variation in sediment brought about by change in agents of deposition, also lead to stratification. Water and wind sort sediments according to size, weight, and shape of particles, and these sediments settle in layers of relative homogeneity. The most common cause of stratification is variation in the transporting ability of the depositing agent. No direct relationship exists between the thickness and extent of strata and the rate of deposition or the time represented for example, a stratum of limestone 2.5 cm (1 inch) thick may take longer to form than a stratum of sandstone 3 m (10 feet) in thickness. A sequence of strata, therefore, may appear as alternations of coarse and fine particles, as a series of colour changes resulting from differences in mineral composition, or merely as layers of similar aspect separated by distinct planes of parting. Stratification in sedimentary rocks may result from changes in texture or composition during deposition it also may result from pauses in deposition that allow the older deposits to undergo changes before additional sediments cover them. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!ĭiamonds may be a girl’s best friend, but what is that mineral’s closest relative? Test your knowledge of rocks, minerals, and all things "yabba dabba doo" in this quiz.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.From tech to household and wellness products. This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Choose a method that best suits your gardening style. You can either use liquid plant foods on a regular basis or controlled-release fertilisers that release nutrients slowly over time. Well-fed plants look healthier, are more productive and are also better able to resist pests and diseases.Reduce the amount of moisture loss by applying a few centimetres of fine bark mulch. Self-watering pots are a great idea as plants will draw on the water supply as needed. If the top layer is dry and dusty, it's time to water if it feels moist and sticks to your finger, leave it a day or so. Potted plants lose moisture much more quickly than in-ground plants so monitor moisture levels regularly.You get what you pay for and a quality potting mix will help your plants grow better for longer. Choose the best-quality potting mix you can afford. Angela Thomas, horticultural communications manager at Yates shares her top tips for using pot plants to create an instant garden courtyard on a patio, or balcony:
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