UPPER, OR FLINTY CHALK. 147 



the siliceous nodules, as they were in the act of separation from the ori- 

 ginal compound mass. The distances of the siliceous strata he imagines 

 to have been regulated by the intervals of precipitation, of the matter 

 from which they are derived ; each new mass, as it was discharged, forming 

 a bed of pulpy fluid at the bottom of the then existing ocean, which being 

 more recent than the bed produced by the last preceding precipitate, 

 would rest upon it as a foundation similar in substance to itself, but of 

 which the consolidation was sufficiently advanced, to prevent the ingre- 

 dients of the last deposit, from penetrating or disturbing the productions 

 of that which preceded it *." 



That the beds of chalk and flint were deposited periodically, cannot 

 admit of the slightest doubt. Specimens are not unusual, in which an- 

 gular fragments of black flint, that could not possibly have been originally 

 formed in their present state, are imbedded in chalk. An example of 

 this kind in my possession, contains several portions of flint which are 

 as sharp and translucent as if recently broken, and entirely destitute 

 of the external opaque crust invariably seen in the perfect nodules ; 

 these are imbedded in, and separated from each other by the chalk. It 

 is sufficiently obvious that the nodule from which these pieces were de- 

 rived, must have been displaced and broken, subsequently to its original 

 formation, and the fragments afterwards enveloped in another and more 

 recent stratum of chalk f . 



* Vide Geological Transactioris, Vol. iv. p. 420. 



t As connected with the history of the formation of sihceous nodules, I cannot refrain from 

 noticing in this place, the extraordinary circumstance of coins, and other antiquities, having 

 been found enclosed in them. 



In Schneiders Topog. Mineral, mention is made of 126 silver coins, that were found en- 

 closed in flints at Grinoc, in Denmark *. It is however much to be regretted, that no descrip- 

 tion is given of the coins, nor any conjecture offered of their probable age ; since, if the account 

 be correct, the determination of that circumstance would fix a certain date to one era, at least, 

 of the formation of flint. 



Mr. Knight Spencer, in a letter published in Bakewell's Introduction to Geology f , relates the 

 following interesting story, and which, from its authenticity, may be considered as decisive of 

 the comparatively recent formation of flint, in certain situations. 



" In 1791, two hundred yards north of the ramparts of Hamburgh, in a sandy soil, M. Liesky 

 of that city picked up a flint, and knocking it against another, broke it in two. In the centre 

 of the fracture he observed an ancient brass pin, and on picking up the other half, he found 



* Phillips' Mineralogy, 2d edition, p. 12. 



■^Bakewell's Introduction to Geology, 8vo. 1813, p. 338. 



u 2 



