As we wished to get to Penzance before dark, should a breeze spring up, we returned on board.  Sailing along very close to the coast, we came off Helston, situated on the inner side of a curious lagoon, separated from the sea by a narrow spit of sand.  Occasionally, in rainy seasons, when the streams which run into the lagoon cause the water to rise to an inconvenient height, so as to flood the shores, a narrow channel is cut in the spit; and the water rushing through it at tremendous speed forms a broad and deep passage, until the lake speedily sinks to its usual level.