LITERARY AND SCIENTIFIC. 365 



lime being separated, takes a solid form, and is deposited upon any substance it 

 may pass over — this was the phenomenon displayed in what was commonly called a 

 petrifying spring. Such springs were not uncommon in this country, as at Ted- 

 stone, near Bromyard, at Castle Froome, and Cradley, Herefordshire, and many 

 other places. Branches of trees, moss, &c. placed in these springs, became speedily 

 incrusted with a thick coat of carbonate of lime. 



The lecturer then entered into a very interesting detail of the calcareous springs 

 of France and Italy, which deposited great quantities of what was called travertine. 

 In central France, where the granite rocks are largely developed, springs of this 

 description, many of them thermal, issue in great abundance. At the base of the 

 hill on which Clermont has been built, there is a thermal spring which has formed by 

 incrustation an elevated mound of solid travertine, 16 feet high and 240 feet long, 

 notwithstanding the continual dissolution and degradation it suffers from exposure 

 to the atmosphere. A thermal spring issues from the summit of San Vignone, a 

 hill in Tuscany, which deposits a layer of travertine half a foot thick annually, and a 

 very compact rock is produced. It extends half a mile in one direction, and 350 

 feet in the opposite one, where it is washed by a river, and terminates abruptly in a 

 precipice 200 feet in thickness. At San Felippo are three warm springs, from 

 which it has been ascertained that a bed of travertine, 30 feet in thickness, has been 

 formed in about 20 years. At this place the water thu« charged with travertine is 

 ingeniously used in a manufactory of medallions. After the grosser parts have 

 subsided, the water is conveyed by pipes to the upper part of a chamber, from whence 

 it falls, and is dispersed in spray over moulds placed for the purpose. These 

 moulds in due time become so thickly coated over, that on being separated, beautiful 

 casts are obtained in white marble. It is curious, too, to learn, that though the 

 moulds may be placed in a highly inclined or nearly perpendicular position, yet the 

 travertine adheres in an equal ratio over the whole exposed surface. 



The lecturer then passed on to a description of the formation of limestone from 

 animal life. Many marine and terrestrial animals constructed habitations for them- 

 selves by secreting from their bodies carbonate of lime ; and shells so formed, were 

 found in such immense quantities as to form the principal part of very considerable 

 mountains. When we considered also the labours of the various coral insects, the 

 formation of limestone was accounted for to an incalculable extent. It was not, 

 however, to be supposed, that the lythophytes added a particle of lime to the quan- 

 tity contained in the mass of the globe, but they certainly caused an accumulation of 

 it upon the exterior. The manner in which the coral tribes raised their curious 

 structures was then described, and the process by which a coral reef was metamor- 

 phosed into a fertile island. Some coral reefs extended from 600 to 700 miles, having 

 a depth of 300 feet or more, so that certain confined seas, as the Arabian and Persian 

 gulphs, were nearly filled up, and navigation much impeded. On the coasts of 

 Malabar, New Holland, and New Guinea, immense masses of coral were stiU 

 forming. Limestone was also formed from the decritus of older rocks of the same 

 material. As the coral insects can only live while in connexion with sea water, 

 should an earthquake elevate a coral reef above the ocean, the living polypes would 

 die, the mass would be rapidly disintegrated, and carried forward by the action of 

 water to new resting places, where covering older rocks, it would thus, in the course 

 of ages, accumulate into a vast deposit, such as we saw in the chalk formation. 



In the Grauwackd series, which immediately succeeded the primary strata, 

 limestone was very extensively developed. The lecturer here exhibited some 

 remarkable specimens from Backberry Hill, a little west of Stoke Park, Here- 

 fordshire. Here was a magnificent exposure of an ancient coral reef, many 

 hundred yards in extent. It was now worked 20 feet in depth, and probably ex- 

 tended several hundred. To the young geologist he should recommend the exa- 

 mination of this hill as a most interesting field of observation ; it was of a circular 

 form, and one of the highest in Herefordshire. Here we saw unquestionable proofs 

 of a tract submerged in the depths of the ocean for thousands of years, and suggesting 

 a train of thought of the most surpassing interest. The Grauwake was then the 

 oldest of the fossiliferous rocks. Mr. Murchison had recently paid much attention 

 to the arrangement of this series, and his labours were worthy of high praise, yet, 

 when that gentleman stated that the fucus serra, and some very imperfect fragments 

 of other fuci were all the vegetable remains furnished by this series, he must be 

 allowed to observe, that other authors gave a much longer list, and as Dr. Fleming, 



