The Boulder Clay is so seldom exposed in the neighbourhood of London, that I think it may be desirable to point out a new locality where I have met with it and where it may yet be seen, especially as I have just found some points, connected with its position at this place, which are of rare occurrence. The new line of railway from Watford to St. Albans passes chiefly through gravel and chalk. At one place, however, called Bricket Wood, about midway between those towns, there is a cutting of some length, and twenty to thirty feet deep, entirely through the Boulder Clay. The superposition of this clay, with regard to the gravels of the London district, is seldom to be determined; the cutting itself throws no light on this subject, or, at least, nothing very definite. But a ballast pit has recently been opened at the Watford end of the Bricket Wood cutting, and immediately south of the line, which exposes a section of much interest. The Boulder Clay has there almost thinned out, leaving but a seam one to two feet thick, whilst both above and below it is a thick bed of gravel. The lower sandy gravel, which consists chiefly of sub-angular flints and flint pebbles, with some quartz, sandstone, and old-rock pebbles, with subordinate seams of whitish sand, has a clean, washed appearance.