part 2] CRETACEOUS AND TERTIARY OUTLIERS. 205 



9. The Petrography of the Cretaceous and Tertiary Out- 

 liers of the West of England. By Percy George 

 Hamnall Boswell, A.R.C.S., D.Sc, F.G.S., George Herdman 

 Professor of Geology in the University of Liverpool. (Read 



June 14th, 1922.) 



Contents. 



Page 



I. Introduction 205 



II. Evidence of the Age of the Deposits 206 



III. Petrography 207 



(1) Cretaceous (Great Haldon, Little Haldon). 



(2) Eocene (?). Marazion. 



Buckland Brewer. 



Great and Little Haldon Hills. 



(3) Oligocene (Aquitanian). Bovey Tracey. 



Petrockstow. 



(4) Pliocene. 



(5) Deposits of Doubtful Age : — 



Puiddaford Water, Bovey. 

 Lustleigh Cleave. 

 IV. Comparison with other British Deposits of Similar Age . . . 224 

 V. Summary of Conclusions 227 



I. Introduction. 



The significance of the outliers of Cretaceous and later age resting 

 on the Palaeozoic strata of Devon and Cornwall has heen frequently 

 noted, especially with reference to the evidence yielded by them of 

 the extent of the great marine transgressions. The details of their 

 petrology, considered in relation to their present altitude and 

 geographical location, are dealt with in this communication, and an 

 attempt is made to throw light on the conditions of their depo- 

 sition and the source of their constituents. Lying as they do, 

 around and among some of the most important igneous masses in 

 the country, they may he expected to afford evidence regarding the 

 stability of detrital minerals and of the source of constituents in 

 sediments of the same age, but of wider geographical distribution. 

 A comparison of the petrography of these outliers with that of the 

 Greensand, Eocene, and Pliocene strata farther east has therefore 

 been instituted. 



These outliers in the West Country may be grouped thus : — 



Cretaceous (Upper Greensand). 



Great Haldon Hills (Devon). 

 Little Haldon Hills (Devon). 



Eocene (PBagshot). 



(?) Marazion, near Penzance (Cornwall). 

 Buckland Brewer, near Bideford (Devon). 

 Great Haldon Hills. 

 Little Haldon Hills. 



