1818.] Mr. Smith's Discoveries in Geology. 361 



principle of selection, for choosing such of the strata out of the 

 great number of others, as should first have colours assigned 

 them, and the tracing and depicting of which on his map should 

 be first attempted. 



5. Having made use of certain strata (selected as above), 

 several of which are very unimportant in almost every other point 

 of view, except in their visible edges, and had not even received 

 a name, or been mentioned in previous geological writings, as 

 the subsequent means of mapping or filling in between the 

 ranges of these characteristic strata, as many of the less conspi- 

 cuous (although, perhaps, more useful) ones * as the scale of the 

 map would admit, a practice at that time quite new amongst the 

 makers of mineral maps, of mine or colliery estates, and even 

 now not adopted, except by those who have expressly followed 

 Mr. Smith in this practice. 



6. Having in these early parts of his survey of the strata of 

 England, by that very particular attention to the nature of the 

 surface soil, and its fitness for, and appropriation to, particular 

 kinds of vegetable cultivation or spontaneous growth, which his 

 previous and early habits as a land surveyor and valuer had 

 led and enabled him to pay to these objects, while investigating 

 the strata beneath, succeeded in ascertaining and establishing 

 numerous helps to the mineral surveyor, from the visible appear- 

 ances of the vegetable productions of a district, towards tracing 

 out the surfaces of its less conspicuous strata beneath.+ 



7. Having, by the same persevering attention to the surface, 

 in connexion with the strata beneath it, ascertained the true 

 source of the supply of all springs of water to be the superficial 

 water (of rains, or streams, pools, &c), percolating downwards 

 through porous strata, or alluvia, until intercepted by water-tight 

 strata, or by faults or patches of clayey alluvia, or by water 

 already stagnated in such porous masses ; and having deduced, 

 and applied in an extensive practice then commenced, these 

 investigations and conclusions, concerning the strata and springs 

 to the draining of land, wherein Mr. Smith has been employed in 

 most of the improving agricultural districts in the kingdom, since 

 about the beginning of this century. 



8. Having, while engaged in the earliest of the investigations 

 above-mentioned, ascertained the important fact of the fossil 

 shells, corals, and other organic remains imbedded in the strata 



» In all the numerous and wide-spread opportunities' which Mr. Smith, Mr. 

 Farey, and others of his friends have had, in seeing the maps which are in the pos- 

 session of the mineral owners, and their lessees and agents, and in those of profes- 

 sional coal viewers, &c. throughout Great Britain, not an instance has occurred of 

 any of these maps depicting the thick rocks and strata, whose edges an- conspicuous 

 on the surface, as the means of marking out almost parallel strips, within which 

 the coals, ironstones, thin limestones, fire-clay, &c. &c are to he found ranging. 

 Although in all the minuliai of surveying mineral estates, these principles and pro- 

 ceedings ef Mr. S. are equally and even more applicable and useful than they are 

 Id kingdom, county, or district surveys. 



t Derby Report, p. I6vi. Phil, Mag. yoI. xxiv. ». 133 ; and vol. xlii. p. 168, 



