82 Geology of the South East of Dorsetshire. 



vol. iv. p. 208, that accurate observer says, " The whole of 

 the Purbeck series is exposed in the ruinous cliffs of Durl- 

 stone Bat/, where the strata have been enumerated in detail 

 by Mr. Webster, (Geol. Tr. ii. 38, 39). 



"At the upper fart they consist of compact limestone, al- 

 ternating with clay, and abounding in fresh water shells, es- 

 pecially of the genus Cyclas: but including also a thick bed 

 called ' cinder' by the quarrymen, which is almost entirely 

 composed of oyster-shells. At the lower part, the formation 

 consists principally of fissile limestone, the junction of which 

 with the Portland strata exhibits some very remarkable ap- 

 pearances. 



" All the stone which is quarried at present, occurs in the 

 upper part of the series ; and from Mr. Webster's list it ap- 

 pears that in a thickness of about 125 feet, 55 consist of beds 

 of useful stone; 12 feet of the ' cinder,' composed of oyster- 

 shells ; and the remaining 58 feet, of slaty clay, and thin beds 

 of unprofitable stone. I was informed that about 150 feet 

 more, of what the workmen call ' rubbish' and ' slate,' inter- 

 vene between the lowest of the courses, (or ' veins') of good 

 stone, and the top of the Portland formation ; so that the to- 

 tal thickness of the Purbeck formation, is about 275 feet," 

 (274 feet 8 inches). What becomes then of Dr. Mitchell's 

 "two sections observed at Durlstone Head in 1833," ? (p. 588). 

 He speaks of 8 and 11 alternations of "stone;" Mr. Webster 

 enumerates and names 52 beds, alternating with clay or shale ! 



Dr. Fitton continues ; — " The high ground between Pever- 

 ill Point and Durlstone Head, is divided by a depression or 

 ravine, on the north of which, in addition to the flexures and 

 contortions seen in all the sections, and well represented in 

 Mr. Webster's plates, the strata are traversed by fissures, pro- 

 duced by upheavings, or subsidence, or both. The effect of 

 these disturbances can be traced by means of the 'cinder' 

 bed; disjointed portions of which are still visible, inclined at 

 different angles, in three or four successive falls, the first 

 throwing down that bed more than 100 feet, and others 40, 

 15, and 3 feet. The fissures which separate the disjointed 

 masses, are widest at the top, and are filled with fragments of 

 the dislocated strata. The place where these derangements 

 occur, is called 'the Gulley:'* on the south side of it the 

 strata are much less disturbed, and the 'cinder' can be traced 

 almost continuously in its proper situation, till it disappears 

 near the face of the hill, not far from Durlstone Head." (G. 

 T. iv. p. 209). 



* This spot is marked in my Fig. 35. 



