160 J. V. ELSDEN — AGEICTJLTUEAL 



protected by an outer coating of flint, it is very durable ; but 

 otherwise it is not well suited for exteriors, as may be seen from 

 an inspection of the west front of Dunstable Priory Church. At 

 the top of the chalk-rock, a hard band separating the Upper from 

 the Lower Chalk, is a layer of phosphatic nodules, containing 

 about ten per cent, of calcium-phosphate. 



From the Eocene beds the most important economic products are 

 the sands and clays, which are extensively used for brick-making. 

 A line of brickfields marks the outcrop of these beds, and they 

 frequently also denote an outlier of Eocene strata lying upon the 

 chalk. The brickfields at Bonnet's End, Bernard's Heath ( St. 

 Albans), and on Berkhamstead Common, are all upon Eocene 

 outliers. 



The sands of the lower parts of the Woolwich and Eeading beds 

 are often of sufficient purity to make them of value for horti- 

 cultural purposes. 



The nodules, known as "septaria," which are of value in the 

 manufacture of Roman cement, occur occasionally in the London 

 Clay, but not in sufficient quantity to make them of commercial 

 importance in this county. ]S"ear Eadlett occur masses of the 

 conglomerate known as Hertfordshire plum-pudding-stone, which 

 were formerly made into querns or hand-mills for grinding corn, 

 for which purpose they were admirably adapted, since the softer 

 parts between the pebbles would wear away a little faster than the 

 pebbles themselves, thus keeping the surface rough. The super- 

 ficial beds yield chiefly gravels, which are used for footpaths, 

 roadways, filter-beds, and in the manufacture of concretes ; but 

 some of the brick-earths are extensively worked for making bricks, 

 tiles, and drain-pipes. 



But although the economic products from the rocks of Hertford- 

 shire are so few and comparatively unimportant, we must not 

 forget that a ridge of Palseozoic rocks extends beneath us, and that 

 the discovery of workable coal in the south-east of England may at 

 some future date alter the whole aspect of the country. Although 

 the borings recently made at Ware and Turnford are against the 

 probability of finding coal beneath our own county, yet our agri- 

 cultural position would be materially influenced by the proximity 

 of a coal-mining district ; for it is the opinion of geologists that 

 coal, if present at all, will be found somewhere between Hertford 

 and Eedhill, resting in isolated patches amongst the folds of the 

 Palseozoic ridge. 



Amongst the economic products it would not perhaps be out of 

 place to mention here the few cases in which medicinal and 

 mineral springs occur in Hertfordshire. But these have already 

 been so fully described by Mr. Pryor that I must be content with 

 a reference to his paper on this subject.* 



* See ' Transactions of the Watford Nat. Hist. Soc,,' Yol. I, p. 109. 



