德文郡的诺瑟姆伯罗斯（Northam Burrows）拥有一道令人印象深刻的海岸防御工事：一道长达2英里、高出高潮线2米以上的石灰岩鹅卵石堤。它看起来像是人工建造的，但实际上是自然形成的，是几个世纪以来波浪作用的结果。
Northam Burrows in Devon has an impressive coastal defence: a bank of limestone cobblestones, 2 miles long and standing more than 2 metres above high tide. It looks artificial, but the bank is natural, made by wave action over centuries.
这道被称为“卵石脊”（Pebble Ridge）的堤坝是海岸巨石沉积的一个典型例子。沿岸漂移将附近受侵蚀悬崖上的岩石向东输送到诺瑟姆伯罗斯。在大型风暴期间，强劲的波浪将石头、砾石、鹅卵石和沙子的混合物推上海滩。
Known as the Pebble Ridge, this is an example of a coastal boulder deposit. Longshore drift carries rocks from nearby eroding cliffs eastwards down the coast to Northam Burrows. During big storms, powerful waves carry a mixture of stones, gravel, pebbles and sand up the beach.
随后，回流会将这些物质带回，但回流的力量不如涌浪强，它会将较小的鹅卵石和沙子带回海滩，而将较大的石头留在高处。
Afterwards, the backwash pulls this material back. But the backwash is not as powerful as the swash and drags the smaller pebbles and sand back down the beach, leaving the larger stones high and dry.
随着鹅卵石海滩的形成，会出现渗流现象，即退去的水通过大鹅卵石之间的缝隙流走，而不是沿着海滩表面流下。这进一步减弱了回流，从而使更多的巨石沉积下来。随着堤坝变得更加明显，渗流作用增强，堤坝最终稳定为一道永久性的屏障。
As a pebble beach forms, there is percolation, where retreating water drains through gaps between large pebbles rather than down the beach. This further reduces the backwash so more large stones are deposited. Percolation increases as the bank becomes more pronounced, and the bank stabilises into a permanent barrier.
“卵石脊”本质上是过去风暴的化石记录，为后方的土地提供了有效的防洪和防侵蚀保护。砾石堤在英国很常见，但英国唯一类似的鹅卵石屏障是多塞特郡的切瑟尔海滩（Chesil Beach）。
The Pebble Ridge is essentially a fossil record of past storms, and provides effective protection from flooding and erosion to the land behind. Shingle banks are common, but the only similar cobble barrier in the UK is Chesil Beach in Dorset.