Geology of the South-East of Dorsetshire. 461 



The wagtails constitute a well-defined and somewhat isolated 

 group, are strictly confined to the older known portions of the 

 globe, and may be said almost exclusively to inhabit the conti- 

 nents of Europe, Asia, and Africa; only two or three species 

 having been found in the islands of the Indian Archipelago, 

 and no example of the form having yet been discovered either 

 in America or Australia. They appear to be naturally di- 

 vided into two distinct sections ; one characterised by a pied 

 plumage, which is subject to a seasonal change, and with a 

 short hind claw ; the other by a more gay plumage, the 

 colours of which are generally olive and rich yellow. In this 

 latter section, the form is slighter in all its proportions, and 

 the hind claw is much produced. The members of the two 

 sections also differ as much in their economy as they do in 

 external appearance; and I am of opinion that Cuvier's 

 generic title of Budytes for the yellow section might be 

 adopted with considerable propriety. 



London, August 16. 1837. 



Art. III. Illustrations of the Geology of the South-East of Dorset- 

 shire. By the Rev. W. B. Clarke, A.M. F.G.S. 



(Concluded from p. 421.) 



We must now revert to fig. 35. and fg. 36. Those 

 sketches may be better represented geologically in the follow- 

 ing section from Tillywhim Quarry (to the westward of 

 Durlstone Head) to Ballard Down, taken from Phillips's and 

 Conybeare's Outlines of the Geology of England and Wales. 



In this figure {fig. 43.), the vertical and curved beds of 

 fig. 37. are represented as connected with the general heave 



Purbeck Hills. Ballard Down. 



Portland 

 Stone. 

 Section from Tillywhim to Ballard Down. ' (Contracted from Phillips and Conybcare.) 



1, Tillywhim quarry. 2, Swanwich. 3, Swanwich Bay. 4, Handfast Point. 



of the inferior formations from under the chalk. Mr. Webster 

 assumes, either that the beds of chalk were formed at two 

 distinct periods, curved strata being laid over horizontal ones, 

 as in fg. 44., and afterwards disarranged ; or, as represented 

 in fg. 45., where the whole of the strata are supposed to 

 have been originally curved, the curves corresponding to 

 similar curves, of which the section fg. 43. gives the 



