INTRODUCTION. 7 



Pholadomya comes a hard band with very large and thick fucoidal markings on 

 the surface, 1 ft. 8 in., followed downwards by alternations of soft and brashy 

 bands and harder bands for a space of 15 ft. Round the corner of the promontory 

 is seen hard nodular material, becoming rubbly below and containing Avicula 

 echinata through 8 ft., beyond which, as the promontory widens, the slabs of 

 true Forest Marble are seen. In this series we can recognise the basal bed as the 

 equivalent to No. 16 of Radipole, and the overlying series as generally equivalent 

 at the two ends. Speaking generally of the deposits, they appear to be divided 

 into two groups : the lower is the specially rubbly bed, about 8 ft. in thickness, 

 without internal stratification, but characterised by abundant Avicula echinata ; 

 the upper is an irregular alternation of hard and soft calcareous brashy beds, about 

 18 ft. in thickness in all, and containing in one bed or another most of the 

 known Ammonites of the Cornbrash of this district. 



In many districts, both in South and North Dorset, whence Cornbrash fossils 

 have been quoted, it is not safe to rely upon them in cases where Forest Marble 

 occurs in the same quarry, or where the basement bed of the Cornbrash is not 

 seen. Those in South-west Dorset records from Punchnowl and Swyre are 

 scarcely available, and any from North Hill, Burton Bradstock, and even 

 Bothenhampton require great caution. In North Dorset, Rampisham now shows 

 only a deserted quarry in Oxford Clay, but any Cornbrash seen there would be 

 available. Nearly the same kind of quarry occurs at Melbury Osmond, but 

 the base is there said to reach the Forest Marble. This is the case also with 

 Corscombe and the quarry at the corner of the road leading up to Closeworth. 

 Similar difficulties appear at Hartington, East Coker, Ryme and Yetminster. 

 We get into contact again with the stratigraphy at Alveston on the road 

 from Sherborne to Holwell. Here a gradient leads down from the Cornbrash 

 to the Oxford Clay, the strata dipping at a higher angle. Along the cross-road 

 from Alveston to Folke is seen a rubbly mass full of Avicula <><-liiixtf<t, and in 

 the slope leading down to the Oxford Clay are two hard dogger bands with 

 intervening soft rubble, eight feet thick in all. These, then, definitely repeat 

 the higher strata of the Weymouth district. 



5. Holwell. — This is an important and instructive quarry situated half a 

 mile west-north-west of the village on the rise of the road leading to Bishop's 

 Caundle. From it a large number of fossils from the Cornbrash, collected 

 by Rev. H. H. Wood, were obtained, which are now deposited in Sherborne 

 School Museum. In it the following strata may be made out : 



Ft. in. 



1. Fine brecciated rubble with solid lumps, Macroeephalites and Terebratulse . 4 6 



2. Solid white limestone with autochthonous fossils, Macvocephalites, etc. . 5 



3. Bubbly rock in several indistinct beds, Avicula echinata, Pholadomya deltoidea, 



and Terebratula intermedia . . . . .50 



