458 PROCEEDINGS OF THE GEOLOGICAL, SOCIETY. [JuilC I9y 



east may be safely estimated at 40 feet. There is anotlier pit at a sliort 

 distance on the north*, and we subsequently visited a third; all of 

 these occupy low ground with respect to Farringdon Clump and Bad- 

 bury Hill ; and taken by itself, the relation of the mass to any of the 

 formations of the district is very obscure. Apart from the organic 

 remains it might be taken for a mass of stratified drift gravel : a geo- 

 logist who should be guided by such characters as those of general 

 aspect, mineral composition, and mode of accumulation, and who 

 finding himself in one of these pits, was required to determine the 

 age of the deposit, might most excusably suppose himself to be in the 

 Crag district of Suffolk : in both accumulations there is a like condi- 

 tion of the mineral materials, a like arrangement of the component 

 beds, and a like proportion, as well as condition, of the included 

 animal remains. In these latter respects the Farringdon beds are of 

 great interest, as they present to us the only instance now remaining, 

 in any part of Great Britain, of a bank of subangular sea-gravel of 

 the secondary period. As compared with the mass of the Crag gene- 

 rally, its condition much more nearly approaches that indicated by the 

 red ; it is however less coarse ; and though the remains of animal 

 structures are in the aggregate equally abundant, the poverty of the 

 Farringdon fauna in species, as compared with any Crag pit, is very 

 remarkable. I am not aware that the collection formed by the whole 

 of our party contained, with the exceptions to be noticed, the shell of 

 a single bivalve or gasteropod mollusk. 



Tereb?'atul(e are abundant ; their valves mostl}^ united, and but 

 little injured, considering the coarse materials in which they occur ; 

 the small urchins (Diadema, Salenid) are also uninjured. The sponges 

 retain their natural forms of growth, with their external characters as 

 distinctly preserved as in recent specimens : it is difficult to deter- 

 mine whether they always occur in their true positions, but most of 

 the larger pebbles exhibit traces that these bodies have fixed them- 

 selves to them, as also have the oysters. On the whole we may 

 safely assume that the various forms lived at the spot at which we 

 now find them — an association not at all at variance with that condi- 

 tion of sea-bed which a pebble-bank implies. If in judging of the 

 depth of water from the sponges which lived about the Farringdon 

 gravel beds, we are guided by the recent and allied forms, such as 

 Halichondria palmata, Tragos infundibuliforme, and T. ventilabrum, 

 we should suppose it to have been about 40 fathoms, and with strong 

 currents. 



The mineral character of the pebbles which compose this gravel 

 suggests considerations of much interest in the history and source of 

 origin of the materials which compose the secondary deposits of this 

 country. The pebbles, as a mass, have been derived from altered 

 sedimentary strata — such as shales converted into flinty slates or horn- 

 stone, and which must also have contained great subordinate veins of 



* This pit was examined by Mr. Sharpe and myself at our second visit. We 

 ascertained here the fact, that the gravel beds rested on the Kimraeridge clay, 

 and with this clue we found that such was also the case with the gravel of the 

 large pit. 



