456 A. J. Jukes-Browne — Lower Qreensand in Dorset. 



so. It seems probable that the insect limestone below the Archseo- 

 niscus bed there is of limited extent, though if pits were opened at 

 the same spot more of the limestone would be found. 



The cutting in the railway close by exposed the Isopod limestone, 

 but no trace of the Insect bed was seen, as the excavation at this 

 spot was not deep enough to reach it. At Chicksgrove, in the large 

 quarry then opened near Tisbury, at the base of the Purbecks, I 

 only obtained one elytron of a beetle, but some ArchcBoniscus very 

 much larger than those at Dinton and Teffont. This may be a 

 new species, but has not been figured or described. It is twice as 

 large as the specimen figured in Fossil Insects, pi. i. fig. 7. Owing 

 to the rough nature of the matrix, probably 'the cap' of the Isle 

 of Portland, these are not so well preserved as those from Dinton 

 and Teffont. This Isopod Crustacean evidently ranged from the 

 base of the Lower Purbecks at Chicksgrove, through the lower part 

 of the Middle Purbecks at Teffont to the upper division at Dinton. 

 In one specimen of ArchcBoniscus from Durlstone Bay, Dorset, the 

 Isopod is lying on its back, showing all the legs folded together under 

 the abdomen, — the only example I ever obtained in this position. 

 The recent discovery by Messrs. Andrews and Browne of Upper 

 Purbecks in the Vale of Wardour, hitherto supposed to be absent, 

 is of much interest to geologists, especially to those who, like myself, 

 have long studied these beds. 



V. — Note on an Undescribed Akea of Lower Greensand 

 OR Yectian in Dorset. 



By A. J. Jukes-Browne, B.A., F.G.S. 



Communicated by permission of the Director General of the Geological Survey. 



UNTIL recently no outcrop of the Vectian or Lower Greensand 

 was known to occur between Lulworth on the coast of Dorset 

 and the neighbourhood of Devizes in Wiltshire. It was supposed 

 that, with the exception of a small area of Wealden in the Vale of 

 Wardour, the whole of the Lower Cretaceous Series in Dorset and 

 South Wilts was concealed and buried beneath the overlapping 

 Upper Cretaceous strata. A recent examination of this district 

 however has revealed two areas where the Vectian sands emerge 

 from beneath the Gault. One of these has already been indicated 

 in the pages of the Geological Magazine;^ the other is the subject 

 of the present communication. 



Eeference to the Geological Survey Map, Sheet 15 will show that 

 the Gault was supposed to thin out and disappear near Shaftesbury 

 so as to allow the Upper Greensand to rest directly on the Kimeridge 

 Clay. This proves to be a mistake; the Gault is continuous helow 

 • the Upper Greensand into and beyond the valley of the Stour. 

 Moreover, two miles south of Shaftesbury and a little east of the 

 hamlet of Twyford a tract of sand emerges from beneath the Gault 

 and forms a terrace which for a little distance has an escarpment of 



^ The Lower Cretaceous Series in the Vale of Wardour, by A. J. Jukes-Browne 

 and "W. E. Andrews, Geol. Mag. for July, 1891, p. 292. 



