338 



Mr. Toulmin Smith on the different Beds 



and Mr. Morris (whose stratigraphical skill is probably unri- 

 valed) as to whether the pits whence the collection was mainly 

 derived were upper or lower chalk, and my own impression was 

 asked. I unhesitatingly pointed out a large number as from the 

 upper chalk, but presently came to some which I was equally 

 clear were from a lower bed *. I was somewhat startled by the 

 information that both groups were from the same pit. A per- 

 sonal inspection could alone be satisfactory. On reaching the pit 

 I found, — and it was fully admitted by both gentlemen, — that it 

 exhibited, exactly in its centre, a clear line of fault, of which the 

 following outline, from a sketch made on the spot, may give some 



Fig. 1. 



idea. I immediately pointed out to Mr. Harris that all his fos- 

 sils of the one group came from the upper part of the chalk on 

 the left hand of the line a — b ; all those of the other group from 

 the chalk on the right hand of that line. As far as could be 

 ascertained from his personal knowledge and from exact inquiry 

 among the workmen, this was found to be the case, and he has 

 since informed me that the suggestion thus made has been of 

 material assistance to him in his subsequent observations. The 

 fact was, that the former side exhibited the upper chalk, the 

 latter much lower beds. Here had been a great fault, so great 

 that these so different beds lay side by side with one another. 

 The whole exposed and unbroken surface of the right-hand side, 

 shaded in the accompanying sketch, was polished and glistening, 

 — as true a case of slickensides as could be found. The attrition 

 had been with such force that several large flints were found 

 actually crushed in the exact line of fault. The band on the upper 

 part of that side is a thin layer of marl to which I cannot now 

 further allude. The rows of flints on the other side are seen in 

 the sketch. 



* I am not, at this time, quite certain whether these were strictly lower 

 chalk or middle chalk forms, and it is immaterial to the present point. 



