332 DR. A. M. DAVIDS AND ME. J. PR1NGLE ON [June 1913, 



Horizon.- — Lower Tremadoc (Shineton) Shales, zone of Bryo- 

 graptus, at depths of 555 and 600 feet, Calvert Boring. 



Specimens in the Museum of Practical Geology, . J ermyn Street, 

 London (26233-4-5, 26355), and in the collection of A. M. Davies. 



IV. The Beetchley Boeing. [A. M. D.] 



Bletchley lies a little over 12 miles from Calvert in an east- 

 north-easterly direction, or approximately along the strike of the 

 Oxford Clay. 1 It is, therefore, of interest to compare the two 

 borings, and see whether that at Calvert may throw light upon 

 that at Bletchley. The latter was described by Mr. Jukes-Browne 

 in 1889. 2 Unfortunately, only fragments of the rocks passed 

 through seem to have been preserved, and no species of fossils were 

 identified. The following is a statement of the strata passed 

 through, condensed from the engineer's section, but expanded by 

 means of Mr. Jukes-Browne's detailed descriptions where necessary 

 for a comparison with Calvert : — 



Thickness Depth 



Nos. in feet and inches. 



1-8. Clay, with some bands of limestone 192 192 



9. Dark -grey limestone, with well-marked oolitic 



structure, echinoderm- and shell-fragments 12 204 



10. Blue clay 8 212 



11. Blue limestone, partly oolitic 5 9 217 9 



12. Blueclay 6 3 224 



13. Light -grey crystalline limestone, very hard; 



echinoderm-fragments 1 225 



14-20. Mainly blue clay, with some limestone-bands and 



septaria 1 131 356 



21. Indurated bluish limestone, very hard 22 5 378 5 



22-25. Sandstone with boulders of granitic rock, and 



beds of clay 31 7 410 



The generally-accepted interpretation of this section is that 

 proposed by Mr. Jukes-Browne and Mr. Cameron, that the upper 

 356 feet belong to the Oxford Clay, and the bottom 54 feet to 

 the Kellaways Kock, the granitic rock (of Charnian character) 

 occurring as boulders in the latter. In support of this view the 

 three main facts are: (1) the similar salinity of the water from 

 the lowest 30 feet, and that from wells in the Kellaways Eock of 

 Bedfordshire; (2) the similarity of Bed 21 to a bed in the Kella- 

 ways Rock of Kempton ; and (3) the fact that the bottom 50 feet 

 of clay (18, 19, & 20) were full of 'just such fossils as would 

 occur near the base of the Oxford Clay.' As to (1), it may be 

 pointed out that saline waters are common in Jurassic rock -beds in 

 •this area ; they have been got from the Forest Marble at Swindon, 



1 [Since the reading of this paper, I have visited the nearest large exposure 

 to Bletchley, that at the Newton Longville brickfield, 1J miles away to the 

 west-south-west, and find ornatum-zone fossils at a depth of about 25 feet 

 below the surface.— A. M. B., April 4th, 1913.] 



2 Geol. Mag. dec. 3, vol. vi, pp. 356-57. 



