﻿Vol. 66.~] species oe ammonites and brachiopoda. 109 



Discussion [on the two foregoing papers]. 



Mr. E. A. Walford stated that he had studied the Dorset sections 

 cited by the Author. The Middle Lias in the Midlands contained, he 

 thought, representatives of the Dorset beds. In the Ammonite 

 fauna there was a complete change from the beds below — signifying 

 a long interval of slight deposition, the full record of which might 

 possibly be found in other countries. In a paper on ' Gaps in the 

 Lias ' the speaker had described the welding of three Liassic zones — 

 Ammonites communis, A. serpentines, and the Transition Bed— into 

 one limestone-block 2 feet thick. Although familiar with the 

 Chideock Hill quarries many years ago, he had not seen the higher 

 Bajocian beds which the Author had described ; and, considering 

 the general fragmentary character of the Inferior Oolite deposits, 

 he thought that it would be wise to restrain much increase of zonal 

 definitions until more was known, and to keep to broad lines. 



Mr. James Paktcer observed that the Author repeatedly referred 

 to the Bridport Sands. He would ask whether these were now 

 reckoned as a geological division. Some forty years ago he remem- 

 bered that, when showing some specimens he had collected from 

 those beds to the late Prof. Phillips, the Professor would not allow 

 the name, contending that Midford Sands had the priority, that 

 name having been given to the beds by William Smith, whom 

 Prof. Phillips looked upon as the father of English Geology. The 

 speaker further said that, in arguing the point, he had considered 

 that the thickness of 150 feet of the bed exposed on the Dorset 

 coast, as compared with the very slight exposure at Midford, entitled 

 the beds to be named after Bridport, just as the clay-beds on the 

 same coast a few miles to the east had received the name of Kimeridge, 

 and that not only in England, but in Erance and elsewhere. He 

 asked whether the Author considered the sands at Bridport to be 

 the equivalent of the Midford Sands. 



The President (Prof. Sollas) congratulated the Author on the 

 very interesting manner in which he had presented a highly 

 technical subject. The correlation of thin seams with thick deposits 

 was a matter of great importance, and called to mind Suess's 

 remarks on the partings in the Trias. It might afford some hints 

 as to the order of magnitude of the scale of time. If we assumed 

 that i foot of sediment might accumulate in a century, in an area 

 of maximum deposition, then in the case of the seam 2 inches thick 

 which was represented by 250 feet in the Cotteswolds, the rate 

 of* formation would be less probably than 1 foot in 150,000 years. 

 In regard to the existence of the numerous zones traced out by 

 the Author, he thought that observation should be extended over 

 wider areas in order to establish them on a firm basis. 



The Author, in reply, remarked that Jurassic zones were by no 

 means the result of local observation only : they had been followed 

 widely, even the new ones ; the thinness of zones was no test of 



