James Saunders — Geology of S. Bedfordshire. 121 



works are enumerated in the list at the end of this paper, the most 

 abundant form being Ostrea vesicularis, var. Baylei. 



On the side of Hart Hill overlooking Luton are some of those 

 terraces or lynchets so characteristic of the Chalk Hills. Other 

 examples exist between Luton and Dunstable, near Chalk Farm, 

 also above the Old Bedford Eoad, near Stopsley ; and again near 

 Chalton on the Lower Chalk escarpment, of which a figure is given 

 in the Memoirs of the Oeol. Surv. vol. iv. pt. i. p. 366, also in 

 the curious valley at the base of Ravensbury Castle, on the border 

 of Beds and Herts. This hollow, in the very heart of the hills, has 

 sides as sharply outlined as though excavated by human agency, 

 and in its extent describes nearly a semicircle. Commencing on 

 a south-eastern aspect, it continues in that direction for a short 

 distance, then turns sharply towards the east, gradually curving in 

 a northern direction, till it eventually opens on the general trend of 

 the escarpment at the village of Hexton, where several springs take 

 their rise. 



Between Luton and Chiltern Green there are several interesting 

 exposures of beds in the Middle and Upper Chalk, along the courses 

 of the G.N.R. and Midland lines, the most extensive of which are 

 those of the latter railway. The first excavation of any extent is 

 about a mile south-east from Luton ; it contains many flints, breaks 

 up into massive blocks, and in the opinion of Mr. Jukes-Browne is 

 to be classified as Middle Chalk. Proceeding in the same direction, 

 the cutting opposite to Luton Hoo Park presents an excellent section 

 of the Chalk Rock, which is usually regarded as the line of demarca- 

 tion between the Upper and Middle Chalk. The beds exposed in 

 this cutting are, in descending order, 



Feet. 



Chalk with flints 6 to 8 



Upper thin seam of Chalk Rock, about ... ... f 



Chalk, intermediate to two seams of Chalk Rock ... 6 to 8 

 Lower seam of Chalk Rock ... ... ... ... 3 or 4 



Middle Chalk, with flints at top 10 to 12 



The Chalk Rock is excessively hai-d, so that, although crowded with 

 fossils, it is difficult to develope them satisfactorily. In some places 

 it is so indurated that it rings almost like flint when struck with 

 a hammer. It is not, however, uniformly compact, for in other 

 places it is easily pulverized. The prevailing colour is grey, some- 

 times merging into a creamy white, and it contains many green- 

 coated nodules. There are two beds often faulted lying approximately 

 parallel to each other, at a short distance apart. 



The Chalk Rock also occurs on the opposite side of the valley 

 at Luton, under the London Road hill. It was customary, some 40 

 or 50 years ago, when lime-works were in operation at this place, 

 for the workmen to drive headings with a rather steep incline into 

 the hill, until the Chalk Rock was reached, when they could excavate 

 considerable chambers beneath it, as it formed an excellent roof for 

 their workings. These tunnels were sometimes driven twenty yards 

 under the hill on the western side of the London Road, and indications 

 of the works may still be distinguished. 



