On the Phosphatic Nodules of the Cretaceous Rock of Cambridgeshire

Abstract

On the twenty-second of January 1868, during the discussion upon Mr. Judd's paper on the Speeton Clay, I was much struck with an observation by Prof. Phillips, that our ignorance of the origin of the phosphatic nodules occurring at many horizons was a reproach to geology. A very short time afterwards the subject was proposed for the Sedgwick prize at Cambridge for 1871; but no essay was sent in. I live in the midst of the so-called Coprolite pits of Cambridgeshire, and have had my attention directed to them continuously for some time, and in May last I communicated to the Society a paper respecting them, with diagrams kindly drawn for me by Mr. Martin, of Christ's College. In consequence, however, of information which has since come to my knowledge, I was led to obtain permission to withdraw this paper, which I now offer afresh, with such alterations and additions as seem to be required. The Cambridgeshire phosphatic nodules, as is well known, are extracted by washing from the stratum (seldom much exceeding a foot in thickness) lying at the base of the lower chalk, and resting immediately, without any passage-bed, upon the Gault. There is, however, a gradual passage upwards from the nodule-bed into the lower chalk or clunch. The average yeild is abour 300 tons per acre; and the nodules are worth about 50 shillings a ton. The diggers usually pay about £140 an acre for the priveledge of digging, and return the land at the end of