148 Geological Society. 



I. lejitorhimis. Also a dorsal fin-spine, with the cartilages to which 

 it was articulated, showing the mechanism of its attachment very 

 clearly. This spine differs from that of /. orthorhinus in being 

 straighter and smoother, and having fewer and smaller tubercles. 

 The author regarded it as probably belonging to /. leptorliinus. 



3. " How the Parallel Roads of Glen Roy were formed." By 

 Prof. James Nicol, P.G.S. 



In this paper the author endeavoured to explain, in accordance 

 with the marine theory of the origin of the Parallel Roads of Glen 

 Roy, the coincidence of the level of these terraces with that of the 

 different cols, and also how the same sea could have produced ter- 

 races at different levels in different valleys. He assumed that, 

 during the gradual elevation of the land, the gradual closing of the 

 straits between its separate masses by the elevation of the cols 

 above the surface would, by checking the eastward flow of the tidal 

 current, cause the sea-level in the western bays to remain stationary 

 relatively to the rising land; and during this period the marine 

 erosion would take place along a line corresponding in level to the 

 col. Hence, in Glen Gloy, which has only one col, the highest in 

 the system, the highest road only was formed ; and Glen Gloy re- 

 mained unaffected by the stoppage of those cols which produced 

 three roads at lower levels in Glen Roy, the lowest of them also 

 extending round Glen Spean. 



March 20, 1872.— Prof. John Morris, Vice-President, 

 in the Chair. 



The following communication was read : — 



" On the "Wealden as a Pluvio -lacustrine Formation, and on 

 the relation of the so-called ' Punfield Pormation ' to the "Wealden 

 and Neocomian." By C. J. A. Meyer, Esq., P.G.S. 



In this paper the author questioned the correctness of assigning 

 the Wealden beds of the south-east of England to the delta of a 

 single river ; he considered it more probable that they are a fluvio- 

 lacustrine rather than a fluvio-marine deposit, and attributed their 

 accumulation to the combined action of several rivers flowing into a 

 wide but shallow lake or inland sea. The evidence adduced in 

 favour of these views was mainly as follows : — The quiet deposition of 

 most of the sedimentary strata, the almost total absence of shingle, 

 the prevalence of such species of Mollusca as delight in nearly quiet 

 waters, the comparative absence of broken shells such as usually 

 abound in tidal rivers, and the total absence of drift wood perforated 

 by Mollusca in either the Purbeck or Wealden strata. 



This "Wealden lacustrine area the author supposed to have origi- 

 nated in the slow and comparatively local subsidence of a portion of 

 a land-surface just previously- elevated. He considered that during 

 the Purbeck and later portion of tlie Wealden era the waters of 

 such lacustrine area had no direct communication with the ocean. 

 The changes from freshwater to purely marine conditions, which 

 are twice apparent in the Purbeck beds, and the final change from 

 Wealden to IS'cocoinian conditions at the close of the Wealden, were 



