Correspondence — Rev. 0. Fisher. 285 



and maintained that the strige observed in chalk are to be regarded 

 as slickensides caused by disturbance and movement of the rock. 

 He described the appearances in detail, and mentioned the occurrence 

 of similar striations in various rocks. 



Discussion. — Mr. "Whitaker said that some of the specimens on the table sent by 

 Dr. "Ward showed slickensides, but that in certain cases the fibrous structure runs 

 through the whole substance. 



Mr. W. T. Blanford stated that he had seen a similar structure in an undisturbed 

 white clay resembling pipeclay, so that he thought the appearance could not be pro- 

 duced by motion. 



The President remarked that the structures brought forward appeared to be of two 

 kinds : first, slickensides pure and simple ; and secondly, fibrous structure, the latter 

 probably due to ehemiciil action, either by an incipient foimation of aragonite, or by 

 the formation of that mineral and its subsequent partial decomposition. 



coi2<i^:Es:poisrx):E3^o:E. 



ON THE CHESIL BANK. 



SiK, — I am glad of the opportunity, given by Mr. Kinahan's question, 

 to explain what I mean by a " drowned valley." I apply this term 

 to an inlet of the sea, which occupies a valley originally subaerial, 

 and excavated by subaerial causes, but into which the sea has sub- 

 sequently run, owing either to a subsidence of the land, or, if such 

 a thing be admitted as possible, by a raising of the level of the ocean 

 at the locality. There are many causes which, to my mind, seem to 

 point to the latter as having really happened. 



In many parts of the English coast old cliffs may often be traced 

 where high ground meets alluvial tracts of salt marsh. I believe 

 them to have been formed during the period of the formation of the 

 Scrobicularia Clays which overlie the submerged forests. These cliffs 

 do not indicate the mode of formation of the bays, which have since 

 become alluvial tracts, but are merely traces of their slight enlarge- 

 ment after the sea had gained access to their areas. 



The order of events has been : — 1. Excavation of the valleys by 

 subaerial causes. 2. Growth of forests now submerged. 3. Depres- 

 sion ; and formation of Scrobicularia Clays and low cliffs — probably 

 the period of the 30 feet raised beaches. 4. Slight re-elevation, and 

 silting up of some of the estuaries (not of all), bringing them into 

 their present condition. 



The reason why I affirm that there were never marginal cliffs to 

 the Fleet is, because I have seen no vestiges of them. The gently 

 undulating surface of the ground declines gradually to the water's 

 edge ; and I have collected fossils from the outcrop of the beds at 

 the edge of the Fleet, where, if there had been formerly cliffs, we 

 ought now to find tumbled talus. Mrs. Bristow's characteristic 

 sketch, in Vol. VI. of the Magazine, gives an exceedingly good idea. 

 of the ground, it being premised that all shown is upland. There is no 

 alluvial ground shown in it. The only alluvial tract is a small part at 

 the extreme head of the estuary, which in the sketch is hidden by a 

 projecting mound. Eeferring to the questions opened by Colonel 



