In mapping the boundaries of the Lias in that part of Yorkshire where the Cretaceous rocks overlap the Jurassic, the Red Chalk becomes extremely useful as a guide, especially as the springs constantly break out beneath it, and give good opportunities for its examination and that of the subjacent strata. Some points of interest have thus obtruded themselves upon one's notice. Its range in Yorkshire may be described as first northwards and then eastwards. Though much covered, by Boulder-clay in the latter portion, it may be traced almost step by step along the former, except where it appears to be absent.