Read it through once

Over the surface of the sand between these upright stems, one often comes upon a most beautiful, glossy, dark-green, velvety cushion. It is composed of a seaweed called Vaucheria, whose twined and interlaced threads form a thick, silky cushion. But it is only beautiful to look at from above. If you pull up a piece of this cushion, you will find that it is growing on black and loathly mud, with many wriggling worms and horrible animalcula. First these pioneer reeds, then this soft, silky carpet of vaucheria, and then the sea-pinks and other estuarine marsh flowers gradually creep forward and extend over the bare muddy sand, so winning it from the sea for the use of cattle.