152 Geological Society. 



The Oxford Clay is represented by grey and blue clays, the 

 lowest bed of which is a hard, tough, brownish clay full of broken 

 shell-fragments : among tbe forms identified from it are Cosmo- 

 ceras sedgwicki (Pratt) and G. stutchburii? (Pratt). 



The Forest Marble consists mainly of grey and bluish-grey 

 oolitic and earthy limestones, with grey, brown, and green clays at 

 the base. An exceedingly bright bluish-green clay, 3 inches thick, 

 is also present. The limestones are very fossiliferous, but the 

 organisms are badly preserved. 



The Great Oolite is represented by grey limestones and grey marly 

 limestones, dark-grey sands, and clays. The highest member is 

 correlated with the ' Cream Cheese' top of the Great Oolite in the 

 Bicester cuttings. From the upper part of the section Terebratida 

 hathonica S. S. Bucknian was obtained ; near the base there is a 

 2-foot band full of EJu/ncJionella and Ostrea. The section is com- 

 pared with the Fritwe.ll-Ardley section on the new railway from 

 Ashendon to Aynho. 



The Chipping Norton Limestones consist of a yellowish oolitic 

 limestone and a grey sandy limestone, also markedly oolitic. 



The Lias is represented by pale-grey shales with very little 

 variation in character. Near the base is a limestone containing 

 fragments of Pakeozoic rocks, aud many fossils, of which the most 

 abundant is Zeilleria waterhousei (Davidson), characteristic of the 

 Jamesoni Zone. This limestone also yielded a derived fragment of 

 Echioceras microdiscus (Quenstedt), a Earicostatimi-Zone fossil. 



In the western boring onlv, strata yielding inflammable gas were 

 met with. Reasons are given for believing that these may have 

 been Triassic. If not, they are probably Upper Paleozoic. _ 



The Tremadocian shales resemble those of Shropshire : their dip 

 varies from 40° to nearly 90°. They show interesting structures 

 resulting from differential movement ; at several horizons they yield 

 well-preserved examples of Clonograptus tenellus, var. callavei 

 (Lapworth) and OboUla (?) aff. salteri Holl. They are traversed 

 by two sills of oli vine-basalt. The uppermost 50 feet are stained 



The following new reading of the Bletchley boring is proposed :— 



Feet. 



Oxford Clay 192 



Forest Marble 33 



Lias (Charmouthian) 185 



An attempt is made to express the depth of the Palaeozoic floor 

 by a contoured map, and its possible constitution and tectonic 

 structure are discussed. 



