[ 81 ] 

 XII. On the LocalUiss of certain ReUqida, or extraneous 

 Fossils, found in Derbyshire. Bij the late i\fr. William 

 Martjh, F.L.S.&c. 



I To Mr. Tilloch. 



N the work, which 1 have recently published on the 

 Petrifactions of Derbyshire*, the localities of the species 

 described are given with as much exactness as appeared lo 

 nie, at the time of writing, necessary for the general infor- 

 mation of the student and collector of these bodies. Thus, 

 in the first part of the volume, I have constantly noted the 

 mineral tract ^ni\ usual geographic situalionf of each fossil, 

 as, <' common in limestone nea. Buxton;' — " found near 

 Chesterfield, in beds of argillaceous ironstone," &o. And 

 in the second part, which contains the systematical ar- 

 rangement of the. species, I have been more particular in 

 pointing out the nature of the seat in which the petrifaction 

 has been found, as " Sedes : strata vetusta, calcaria." — 

 "Sedes: strata vetula, argillacea, ferrifera," &c. &c. It 

 has occurred to me, however, since the volume was printed, 

 that something- more might have been added, with advantage 

 to this part of the undertaking; and that, in a geological 

 point ot view, notices of the particular situations, {tocaspe- 

 cialia,) as well as of the immediate stratum, in which the 

 fossil has been discovered, will be found useful appendages 

 lo the specific diagnosis, or general description of the species. 

 All, who have attended to extraneous fossils in the f eld, as 

 well as in the cabinet, must have observed, that the different 

 species, as I have elsewhere remained X, abound in particular 

 K"cks, especially of those which are properly denominated pe- 

 trifactions, and though not wholly confined to, are more com- 

 mon Ml, particular sirata than in others, though of the same 

 substance and constituting a part of the same lof/, or series of 

 mineral beds : thus in Derbyshire the shells, corals, &c., 

 which abound in the first limeslojie stratum, or that which 

 immediately follows the shale tract, are by no means frequent 

 ■in the second limestone, or that which lies under the first 

 toad:ttonc. Nor are the petrifactions of the second limestone 

 common to \\\q first or third, &c. ; though all these strata 

 arc evidently constituent parts of the same forniation. 

 Again, in the coal soils of this'county the constituent strata 

 ot gritstone, ironstone, shale, &c. may all, I think, be 

 characterized by their respective vegetal fossils. That 

 much practical utility in geology and mining might be the 

 result of this circumstance, when the different species of 



• PelTifcata Derbimsia, or rig-ures and Descriptions collected in Derbyshire, 

 t lor the particular sense, in which thee terms are here eni.ioVed, I 

 must refer to the " Outlines," &c. pp. 15J. I81. \ Outlines, p. 9. 



Vol. 39. No. 166. Feb. IS] 2. F extra- 



