186 MR. W. J. LEWIS ABBOTT ON THE [May 1 894, 



pebbles, none of which exists in the sandy beds above the fissure ; and 

 from the Gault Clay pools were derived in times of flood the large 

 quantity of CAara-stems. It thus appears impossible for the filling 

 in to have resulted from marine submergence, or for the material 

 to have been introduced in the form of a land-wash from above. 



2. That the deposit was introduced into the fissures by a river is 

 to my mind evident, from the fact that the material itself is exactly 

 similar to that deposited in other sequestered spots in the valley, 

 and the additional fossils constitute just such a heterogeneous mass 

 as is to be found in the burdens of a river when preserved, and 

 nowhere else. That water was present during deposition appears 

 evident from the horizontal stratification of the sand and clay, and 

 the scales of slow-worm and Chara- stems adhering in a straight line 

 along the walls of the fissure ; while the manner in which the 

 fissure-material was forced upwards into blind veins and crevices 

 from below is explicable on no other than an aqueous hypothesis. 

 That the river was entering at the sides of the valley during a long 

 period in the history of the filling of the fissure is absolutely certain 

 from the damming action of the keyed stones, and the deposition of 

 the material in passing round such large blocks. 1 



Coming to the mollusca, Helices, Pupce, and the others are always 

 found in river- deposits, and such forms as Succinea are never found 

 far from water, but usually in it, while Unio is never found 

 elsewhere. The preponderance of frog-bones over everything else, 

 the large number of water- and bank-voles, the presence of Chara 

 in such profusion, entomostraca, and Triton unmistakably point, in 

 my opinion, to the fissure-deposit having had a river origin. 



3 and 4. In the keyed stones, as it appears to me, we have an 

 absolute answer to the question of the reopening of the fissures. 

 We have seen that the keyed stones occur all through the deposit, 

 into which position they were let fall, by the fissuring of the strata 

 (or some may have been dislodged from the mother-rock by the 

 entering of the water during the process of filling). It was in this 

 keyed condition that they were when the deposit successively reached 

 them. As the fissure filled the material became packed closely all 

 round and over them, the inward transport of larger burdens being 

 intercepted by these obstacles ; and just as the material was originally 

 deposited, so we find it to-day. Had a subsequent widening set in 

 every stone originally keyed would have been loosened from the 

 grip, and a keyed stone would have been practically an impossibility. 

 It might, however, be urged that, by an unprecedented series of 

 coincidences, every stone was so placed that when its hold was 

 broken it ploughed through the solid material until it again became 

 keyed, or fresh ones got into that condition. But if this were the 

 case, and the stones moved out of their original position, all former 



1 Very careful and protracted observations lead me to consider that the 

 •downthrow of the valley did not occur till just immediately after the river had 

 entered the Hythe Beds. 



