The writer has for some time hesitated to seek in the pages of the Geological Magazine a publication of his-experiences upon the above subject. He fell last year into a grievous mistake with regard to it, and suffered that mistake to be published in the “Transactions of the Devonshire Association for the Promotion of Science, Literature, and Art.” It will be his duty, when the opportunity comes round (as shortly it will), to call attention to that mistake in the pages of the same periodical. In the meantime he thinks that the subject, and even the mistake associated with it, may be of something more than local interest. At least the recantation of a published error cannot be too widely circulated.