602 Limestone Quarries and Petrifying Spring 



quarrymen term them*; the lower green-sand, the first marine 

 bed above the Wealden, rests conformably on the clay, and 

 the change from the deposition of the freshwater remains to 

 that of marine shells appears to have been " effected," ob- 

 serves Dr. Fitton, " simply by a tranquil submersion of the 

 land to a greater depth beneath the surface of the waters." 

 The remains in the Purbeck strata, below the Hastings sands, 

 are, for the most part, freshwater ; but a singular exception 

 occurs in the middle of the bed, in a layer of oysters 12 ft. 

 thick : oysters, however, as is well observed by Dr. Fitton, 

 are well known to inhabit estuaries within the range of fresh 

 water. The Portland strata, immediately below the Purbeck, 

 may be said, for the depth of 10 ft., to be composed of thin 

 layers of compact slaty limestone, down to the famous " Dirt- 

 bed," in which are found the remains of large groves of trees, 

 some of which are prostrate, some inclined at various angles, 

 and many again with their roots firmly fixed in the black soil 

 in which they originally grew, their trunks and branches, 

 stretching upwards through the freshwater strata above, re- 

 sembling, in this respect, the various subterranean forests 

 found round about the sea-coast of Great Britain, as well as 

 on the shores of the north of France ; save that the trees, in 

 the latter instance, belong, for the most part, to existing spe- 

 cies, while those which occur in the " Dirt-bed" are no 

 longer met with in any part of the globe. From the 

 stumps of these trees remaining erect, Dr. Buckland and Mr. 

 De La Beche have inferred that " the surface of the sub- 

 jacent Portland stone was, for some time, dry land, and covered 

 with a forest ; and probably in a climate such as to admit the 

 growth of the modern Zamia and Cycas." +■ The " Dirt-bed " 

 is succeeded by a stratum called " Top-cap " by the quarry- 

 men, 1 ft. thick, and having very much the aspect, according 

 to Webster, of freshwater limestone : it contains, however, no 

 fossils. The remains of the next and subjacent beds are ex- 

 clusively marine. Whether this very curious alternation of 

 marine and freshwater remains was produced by the elevation 



* Dr. Fitton mentions a fault in the limestone, sixty fathoms deep; 

 he however does not give the locality, and I enquired for it in vain of the 

 workmen, in my rides to the different quarries within 20 miles from Has- 

 tings. The workmen wholly disbelieved its existence, and evidently con- 

 sidered I was hoaxing them when I mentioned it. 



t See abstract of the paper from which this passage is taken, Geo/. 

 Soc. Proceedings, April, 1830, p. 218, 219.; and Phil, Mag. and Annals, 

 vol. vii. p. 454. The details will appear in Dr. Buckland's Memoir, in the 

 fourth volume of the Geol. Transactions, now in the press ; in which also 

 will be published Dr. Fitton's long expected paper, " On the Beds beneath 

 the Chalk," &c. 



