66 MESSES. W. E. ANDREWS AND A. J. JUKES-BROWNE [Feb. 1 894, 



Middle Purbeck. — Basing this upon the brown and black clay 

 seen at Teffont and at Chicksgrove, it will be found that, though the 

 thicknesses of individual beds in the two sections vary, the vertical 

 distance from the basal clay to the top of the Cinder-bed is almost 

 exactly the same in both, namely, a little over 12 feet. The great 

 cutting on the line south of Teffont shows 19 feet of strata above 

 the Cinder-bed, and if these lie entirely below the clay and sand of 

 the Dinton cutting there is that much (and possibly more) to be 

 classed as Middle Purbeck, for we have no complete section of this 

 part of the series. A total thickness of 32 feet is therefore probably 

 below the mark. 



Upper Purbeclc. — The clay and sand in the Dinton cuttings must 

 be from 18 to 20 feet thick, and between the top of this sand and 

 the top of the second seam of calcareous grit there is at least a 

 thickness of 8 feet. This grit forms the floor of the Dinton well, 

 which is about 40 feet deep. Hence there is at least 66 feet of this 

 division, and how much more lies beyond we do not know — probably 

 more than 2 and less than 12 feet; but, taking the former figure, we 

 have a minimum thickness of 68 feet. 



Putting the estimated thickness of the three divisions together, 

 we have — 



Upper Purbeck 68 feet. 



Middle Purbeck 32 „ 



Lower Purbeck 70 „ 



170 feet. 



Considering the distance that intervenes between the Vale of 

 "Wardour and the coast of Dorset (about 32 miles), it is really re- 

 markable that in a set of estuarine and freshwater strata there 

 should be so close a correspondence between the two series that 

 many of the subdivisions which have been recognized in the Dorset 

 sections can also be distinguished in Wiltshire. The Wiltshire 

 Purbeck strata do not in fact differ from the typical facies of 

 Durleston Bay to any greater extent than those of the Upwey (or 

 Bidgeway) section do. 



The first point of similarity is that within the small area of the 

 Yale of Wardour the basement-beds show a variation similar to 

 that which occurs in Dorset, but only at sections some distance apart. 

 The basement-beds at Chilmark resemble the ' Cap ' of the Isle of 

 Purbeck, but the basement-beds at Chicksgrove and Wockley re- 

 semble those at Upwey, where the lowest Purbeck bed is a limestone 

 about 1 foot thick, separating into three layers, the highest of 

 which contaius fish-remains (Hislionolus breviceps), the second a 

 large Archceoniscus, and the lowest Cyprids and Pcdudina. This 

 rests on soft, sandy limestone-with-fiints, so that the succession is 

 not the same, although similar. 



The next noticeable resemblance is the occurrence of broken-up 

 limestone and contorted marls, which seem to occupy the place of 

 the ' Broken Beds ' of Dorset. These are also succeeded by a set 

 of beds in which Gypris purbecJcensis is abundant, and are therefore 

 comparable with the ' G'^/pm-freestones ' of Dorset. The Bidge 

 beds, with their abundance of Cardium, Corbula, Leda, and Serpula, 



