7. Railroad Sections. From the uncertainty of the tide levels, and the inherent defects of the methods, both trigonometric and barometrical, by which most of the heights above mentioned were obtained, they cannot be absolutely depended on within a few feet. Those given in the sections of the numerous railroads through England, having been ascertained by levelling, are much more to be relied upon: they are, probably, as accurate as any that ever have been obtained in undertakings not expressly directed to scientific purposes; and are the more valuable, as the two other modes of measurement are most erroneous when the elevations are small. In the course of a few years the entire surface of this country, wherever the introduction of railroads is practicable, will thus be covered with a network of intersecting lines, along every one of which the heights will have been determined to within a few inches of the truth. A well-arranged collection of the levels will then form a very useful compilation to inquirers in various departments of physical science; and it is to be hoped that some person properly qualified, who has leisure for such a purpose, may be induced to enter upon the undertaking*. The following Lists contain only the approximate height of a small number of points, along the principal lines of railroad in that part of the South-East of England which is represented in the map, Pl. IX. The first two cut through the chalk range of the midland counties, in passing from London ;-1. North-westward, as far as Stony Stratford;-2. By Reading, through the defile of the Thames, towards Abington; and thence, westward, to the vicinity of Chippenham. 3. The South-eastern line, after passing the chalk near Godstone, descends the Valley of Kent, by Tonbridge and Ashford, to Folkstone and Dover. 4. and 5. The Brighton lines traverse the chalk downs and the Wealden denudation, southwards, between London and the Sussex coast. 6. The Southampton railroad crosses the continuation of the anticlinal line of the Wealden towards the Vale of Wardour, and connects the basins of London and the Isle of Wight. I.-HEIGHTS ON PART OF THE LONDON AND BIRMINGHAM RAILWAY+. The Datum in the Section of this Railroad, Datum below the Trinity high water mark, at In the present unfinished state of the works, the attempt would be premature; but when the railroads have been completed, the several lines will furnish admirable facilities for accurate levelling along them, and for connecting the heights in the interior of England, with fixed and durable standards at well-chosen places on the coast, the height of which above the sea, may be afterwards ascertained by long-continued observation. From the first of these operations, we should obtain the relative height of a number of points, any one of which might be taken as a standard, and all of which are, probably, themselves in motion, and may be expected to differ in elevation after the lapse of years. On this account, the multiplication of standard marks, both inland and on the shore, is very desirable; while the latter should be compared, from time to time, with the supposed invariable mean level of the sea. The height of the tides themselves, however, is in some degree affected by the features of the coast, which it is well known to geologists, are in a state of constant and even rapid alteration. + Where roads, canals, and streams are mentioned in these lists, the points referred to are those of their intersection by the railway. The names of the places are in the Ordnance Maps; and the precise points are indicated by reference to adjacent words, letters, or objects on the map. II.PART OF THE SOUTH-WESTERN RAILROAD; LONDON TO BRISTOL. The former terminus, or starting point, of this road, was on the Birmingham railway, about a mile west of Kensal Green. The present terminus is at Westbourn Green, about mile north of Bayswater, on the Uxbridge road from London. The Datum, or base, of the Section is supposed to be about 7 feet above the Trinity high-water mark, at the London Docks. [Therefore, (approximate) height of the datum, above low-water mark at Sheerness is (19-6699+7)= 25.6699 feet.] Paddington Canal, at the north-west angle of Old-oak Common.... 247.75 Railroad at the entrance of the Tunnel on the east; south-east of the 36th milestone 126 Highest ground over the Tunnel near its western extremity 193 River Kennet, near Broken-brow, north-west of letter B; about mile east of Reading 98 General level of the Valley of the Thames, from Broken-brow to near Kentwood, about........ 100 85 Brent River at Hanwell, south of letter H... Road from London to Uxbridge, near the cross road from Greenford to Norwood and Osterley Park 14 65 ..... Paddington Canal, east of letter Y in Yedding Brook 84 Grand Junction Canal, near Botwell ..... River Colne, near W. Drayton; west of the words Colham Mill General level of the surface, on the line from near Southall, to the heights over the Valley of the Thames, east of Maidenhead Bridge. Road from Slough to Stoke Poges; about mile from the cross roads ........about Cross road from Amerton Bank to Taplow, about 24 miles from London, on the road to Maidenhead 84 68 Highest point of ground over the Tunnel near Purley; south of east of the words Purley Hall......... 253 Road about 4 miles from Reading to Pang bourn, north of y in Purley Hall 147 Thames River, about mile north by east from Moulsford Church, Berks ....... 117 90 Highest ground over the line of railroad, between the Thames and West End, on the south-west of Cholsey Field............ Paper mill stream, north-east of South More ton; and north-west of P in Paper 195 134 90 III.-ON THE SOUTH-EASTERN RAILWAY, FROM LONDON, BY TONBRIDGE AND ASHFORD, TO DOVER. Road to Woldingham Church, about 4 mile south of the Church..... 790 Road from Sellinge to Hythe, about mile from Grove Bridge over the Stour... River Stour, south of Stanford Church, about 14 mile from its source near Postling...... 230 Summit of the sand heights cut by railroad near Stone Farm 193 325 277 Stream at Beachborough, nearly south of the summer-house, 0.3 mile west of the word 188 224 106 River Medway, south-west of Powder Mills,| and 1+ mile from Tonbridge; west of the y in Medway 60 General level of surface, from the road east of Tudely church (70 feet), to a road west of Hoghill Green (53)......... Main road from Tonbridge to Tonbridge Wells; about 4 mile from the separation... to Hastings... 67 60 79 Road at Rat's Castle, on the eastern verge of Paddock Wood Streamlet (valley of the gault), about mile from Inbrook, south of St. Thames's Well. Ground at base of Martello Tower, No. 1.... 241 [The same place above low-water, barome...........F. 261 465 trically Deduct diff. of tides, (at Folkstone)... 21 240] Height of the chalk cliff, at the beginning of the undercliff east of Copt Point...... Height of proposed termination of the railroad, near the Arch-cliff fort, Dover; 58 miles 7 furlongs from London 107 A change 83 IV. SIR JOHN RENNIE'S LINE OF RAILROAD, FROM LONDON TO BRIGHTON. 397 Road (above the proposed Tunnel) from the Turnpike to Dean's Farm; about three fourths of the distance from the Turnpike road Highest point of ground over the proposed Tunnel at Merstham Hill; about 4 furlongs south of the point last mentioned... 498 Turnpike-road north of Merstham, at the Jo liffe Arms, north of the letters ge in Parsge.. 363 Ground near the Windmill, Merstham, on the ridge of the Upper green-sand (fire- 362 stone) Millstream, west of the bottom of letter M 285 in Mill Stream, where cut by a line from the top of 232 the letters in the word Linkfield...... Road from Nutfield to Reigate; immediately 238 on the south of the second a in Tanyard. Stream tributary to the Mole, between the two letters B in Bonehurst Bridge. [From the brook at Bonehurst Bridge, to that north of Hazlick Mill (more than 4 miles), the surface is nearly flat; on the Weald-clay.] Brook, about 2 miles south of the place last mentioned; above the second letter e in Horley-lane Farm ...... 152 165 Lane dividing Surrey and Sussex; south-west of the second a in Oakland. Stream at Hazlick Mill; where crossed by the road from Jordan's Farm to Wakeham's Green 145 154 ....... ..... 217 254 River Mole, near the road from Crawley to the Workhouse, south of the letter g in Three Bridges [Near this place, the ground begins to rise into the Forest ridge, (Hastings-sand).] The Mole river, in Tilgate Forest; on a line with the word Tilgate, and north-west of letter C in Cinder Banks Ground in Tilgate Forest, about half a furlong north of re in Green Trees Ground over a proposed Tunnel through the summit of Balcombe Down; (about a furlong east of the letter B in Balcombe) Road from Cooper's Corner to Balcombe Church; at the letter e in Cooper's......... 293 [A rapid descent of very irregular ground succeeds.] 304 439 Height above the Datum. Stream of the Ouse River; immediately on the south of the letters and s in Pilsty......... Highest point of ground over a proposed Tunnel through the heights north of Cuckfield; about half a mile south of letter a in Taylor's Barn......... [Irregular ground, rapidly declining, succeeds for about 2 miles.] Stream of a large branch of the Adur; about 2.1 miles directly south of the bottom of letter E in the word CUCKFIELD, and about 2 miles west of Wivelsfield ....... [The surface here for about 4 miles is very irregular; the greatest height, about 250 feet; the average, 80 to 100.] Stream, south of the letters Oa in Friar's Oak V.-MR. STEPHENSON'S LINE OF RAILROAD, FROM LONDON TO BRIGHTON. 128 bowl Road from Dorking to Reigate, at the crossroads south-east of the words Punch Bowl 184 Highest ground over a proposed Tunnel, about 0.35 mile from the cross roads last mentioned; south-east of G in DORKING... 345 Height of the bottom of Tunnel at its exit... 82 Lane or road, west of letter P in Park Farm 218 Stream between two lanes north of letter S in Scammet's Farm ...... Stream (another tributary of the Mole, springing on Holmwood Common); at a point south of the second m in (Brockham) Common 165 Highest point of ground over a Tunnel through the ridge on Epsom Common; 0.1 mile due south of the second m in the word Common Height of the railroad at the exit of the Tunnel........ 207 Height, in the wood, between the words Henfold and Park Gate 285 156 Streamlet on the south of the wood, due east of the word Knole Farm ....... [The highest point of the railroad hereabouts, is between the streamlet last mentioned and the village of Newdigate, and is 247 feet above the datum. The road then declines rapidly to Warnham, and thence to the seaside.] 221 |