406 Bev. T. G. Bonney—On the Roslyn Hill Clay Fit 



faulting, accompanied by a dragging down near the fault, an 

 ordinary " downthrow" would be required here, not a reversed fault. 



Passing eastwards along the wall of Kimmeridge Clay, we now and 

 then notice a slight appearance of dragging down, which of course 

 would be compatible with either a fault or a line of old cliffs, from 

 which slips had taken place on to the bed of a valley-; but as the 

 beds forming the floor of the pit show no traces of any disturbance, 

 I consider this as no evidence for the fault hypothesis. At the south- 

 east angle we have the sequence represented in Fig. 1. Beginning at 

 N. end, the Lower Chalk, marly, and showing traces of bedding, dis- 

 tinctly dips at an angle of about 30" to N., the Upper G-reensand with 

 phosphate nodules and characteristic fossils is in its usual place below, 

 and the Gault (with many phosphatic nodules and fossils) below that ; 

 and then the Boulder -clay distinctly dips under it at about the same 

 angle. Here then, if there be a fault, we have a still more sin- 

 gular case of a reversal. The Boulder-clay, on the occasion of my 

 last visit, showed most singular contortions,^ various chalky and 

 sandy layers being crumpled up in the strangest manner. The clay 

 at the southern end is full of blocks of Neocomian sandstone, which 

 from their position have evidently slipped from above. Mr. Seeley's 

 section ofthisendof the pit (Geol. Mag. Vol. V., p. 348) is certainly 

 wrong; the Brown sand which, with superjacent Gault, he brings 

 down between the Kimmeridge Clay and Boulder-clay at the S. corner 

 is not in situ, but has fallen from above. I have no doubt on this 

 point, as I have watched the section for nearly four years, and seen 

 that the Neocomian stratum was merely a number of boulders included 

 in the clay, and on the last occasion almost all of them had been re- 

 moved, I can only explain the mode in which these blocks occur 

 by supposing, that before and during the accumulation of the 

 Boulder-clay, there was nearly along the line of the south side of 

 the pit a cliff or bank of Kimmeridge Clay, capped by Neocomian 

 rock, from which fragments slipped and fell. 



We will now turn back a short distance. About a year ago I was 

 fortunate enough to see a large portion of the pit-floor in the south- 

 east corner laid bare (which is now converted into a pond). This 

 showed me the Gault resting on the Boulder-clay, and the latter in 

 apposition, as described above, with the Kimmeridge Clay, without 

 the intervention of any Neocomian sand. I also saw a large fragment 

 (several cubic feet) of Kimmeridge Clay inclnded in the Boulder-clay 

 near the south-east corner. On examining the floor of this new ex- 

 cavation, I found that the Kimmeridge' Clay and the Gault gradually 

 approached one another, so that at about 60 paces from the end of 

 the pit they met, as represented in Fig. 2 ; this might still be seen 

 when I was last there, in a bank which had been left for a dam. 

 Laying down the results of these four sections (Figs. 1 — 4) on the 

 sketch-plan (which does not pretend to be much more than a diagram, 

 the form of the pit being very irregular in its minuter details), and 



^ This crushing appears very local, because on other occasions it was far less 

 marked ; and I do not regard it as in any way indicative of a fault, rather such as 

 might be caused by melting of included ice-blocks or local settlements. 



