238 



35. — Miscellaneous Is'otes and Obseevations. 



[Read 4th June, 1877.] 



Geology. 



The Coprolite Beds at Hinxivorth. — My property in the parish of 

 Hiiixworth, the extreme nortliern boundary between Herts and 

 Beds, is on the geological formation containing the now well- 

 known Cambridgeshire coprolite bed, or, geologically speaking, 

 the Cretaceous phosphatic nodules which are found in a thin seam 

 of the Upper Greensand at the point of contact of the Chalk Marl 

 with the Gault. In the years 1856-8 Mr. B. Denton carried out 

 some di-ainage works for me in the parish of Hinxworth, over an 

 area of 800 acres, the progress of which was fully reported by him 

 in the 20th vol. of the ' Journal of the Eoyal Agricultural Society ' 

 (p. 273), where he thus described the geological character of the 

 district: — "The estate lies at the bottom of the Chalk escarp- 

 ment of the London Basin, and covers a portion of the lowest 

 bed of the Chalk, the outcrop of the Greensand, and a portion 

 of the Gault of the Greensand formation. In several parts 

 a superficial deposit of drifted gravel and sand overlies the older 

 beds. The Greensand separating the Chalk from the Gault is very 

 thin, and, if collected in a distinct layer, would not exceed thi'ee 

 inches in its thickest part." As I then myself occupied, and con- 

 tinued to occupy for some years later, 300 acres of the land lying 

 upon the Gault and thoroughly drained, I necessarily became 

 aware of the existence on my own property of the seam which 

 contains the copi'olite bed. The discovery by Liebig of dis- 

 solving bones in sulphuric acid for the purposes of manure had 

 at that time given a commercial value to these phosphatic nodules, 

 and they were eagerly sought for by the manufacturers of mineral 

 phosphates for agricultural purposes. 



The origin of these nodules appears still to be a questio vexata. 

 An exhaustive paper " On the llclations of the Cambridge Gault 

 and Greensand," by Mr. Jukes-Browne, was read in 1875 before 

 the Geological Society, and appears in the 31st vol. of the Journal 

 of the Society (p. 256), with a map which shows the course of 

 the strata which contain tlie seam, between Tring and Cambridge, 

 In this map the name of the parish of Hinxworth docs not occur, 

 but its position is on a projecting point of the Gault between Arlesey 

 and Ashwell. This and other papers lately read before the Geo- 

 logical Society by Messrs. Jukes-Browne, Fisher, and Bonnoy, still 

 leave open the question whether the phosphatic nodulos "originated 

 where they are now found, or have been derived from the under- 

 lying Gault." As regards the yield and money value of these 

 nodules, some of these papers give the average yield as 140 tons 

 per acre and 50s. per ton value — tlie land to be restored to its 

 original level and condition by the contractor. The value of the 

 seam, however, necessarily depends upon tlie depth below the 



