hertfordshire natural history society. xxxv 



Field Meeting, 24th May, 1880. 

 AYLESBURY, IIARTWELL, AND STONE. 



Altlioiip;li this meeting, which took place in conjunction with the 

 Geologists' Association of Loudon, was the annual whole-day 

 meeting, and might therefore seem to warrant a full report, the 

 locality in which it was held being outside the limits of our county, 

 and a complete account of the proceedings of the day, by Mr. W. 

 H. Hudleston, the director of the meeting, having already been 

 publislied, a very brief notice will here be given, and Mr. Hudle- 

 ston's report in the ' Proceedings of the Geologists' Association ' 

 (vol. vi, p. 344) may be referred to for a detailed account of the 

 geology of the neighbourhood, full descriptions of the sections 

 examined, lists of fossils, and an exposition of the most recent 

 views as to the origin and relations of the various beds. 



On arriving at Aylesbury, Mr. Hill's brickfield in the Bierton 

 Road was first visited, and here the Kimraeridge Clay was seen, 

 with the basal conglomerate of the Portland series reposing upon it 

 in one part of the pit. Proceeding towards Hartwell, beds of the 

 same geological age were seen in Mr. Locke's brickyard, the clay 

 here being termed the Hartwell Clay, and the base of the Portlands 

 being represented, as usual in this neighbourhood, by the lydite 

 series, here more calcareous and less glauconitic than at Aylesbury. 

 The Hartwell Clay appears from its fossils to occupy a higher 

 horizon than the Kimmeridge Clay at Oxford, representing more 

 nearly the Middle Portlandian of Boulogne. At the "Bugle" pit 

 near Stone, which was next visited, the junction of the Portland 

 limestone with the Purbecks was seen. From the limestone here, 

 which appears to be higher in geological position than the Portland 

 beds at Aylesbury, most of the ammonites {Ammonites houlogniensis) 

 which were seen built into the wall of Mr. Lee's park have been 

 obtained. 



The "Round Hill" was then ascended, and on the summit, 

 from which a fine view of the Vale of Aylesbury was obtained, 

 Mr. Hudleston pointed out the relation between the physical 

 features of the valley and its geological structure. The concluding 

 portion of his remarks, in which he speculated on the possible 

 shore-lines of the Portland seas, will be of interest in their bearina: 

 upon the early geological history of Hertfordshire. " The remiirk- 

 able analogy whirh," he said, "in some respects the Portland 

 beds of Bucks present to those of the Boulonnais, which all 

 geologists agree were deposited not far from a promontory of the 

 old Ardennes ridge, might lead to the supposition that the 

 influences of such a ridge, even if not actually above water, have 

 made themselves felt in the migrations of Mollusca, and also in 

 the nature of the deposits, though those of the Boulonnais are 

 even more sandy than in Bucks, where there is at least one 

 tolerably pure limestone. Prom recent borings the undulating 

 character of the old Palaeozoic floor, upon which the Secondary 



