182 



LIAS OF DORSETSHIRE. LIAS OF FRANCE. 



ally, surrounded by stone harder than the other part of the stratuni, 

 and project above the surface. At Sandsend, near Whitby, the alum 

 shale has been perforated near the sea, lo the depth of one hundred 

 and thirty yards, without penetrating into the subjacent rock ; to 

 which if we add the height of the cliffs above, it will make a total 

 thickness of lias exceeding two hundred and twenty yards : the up- 

 per parts are more productive of alum than the lower.* In Dorset- 

 shire, the whole thickness of the lias formation may be seen in succes- 

 sion : a few miles west of Bridport, the uppermost bed rises above 

 the level of the sea ; and three miles west of Lyme it terminates, 

 and the white lias (the lowest part of this formation) may be obser- 

 ved at low water resting on red marl. 



The lias formation is extensively developed on the eastern side of 

 France. In passing by Rouvray to Dijon, in the year 1820, I was 

 exceedingly struck with the complete resemblance of the geology of 

 the country, with that of Leicestershire and Worcestershire. Be- 

 fore arriving at Rouvray, we pass over red marl 5 after leaving that 

 town, the road traverses a very low range of decomposing sienite and 

 granite rocks, exactly similar to those of Malvern 5 after which it 

 passes for several miles over well characterized lias, filled with gry- 

 phites and belemnites : masses of the harder parts, filled with these 

 fossils, are collected for keeping the road in repair. 



In England, lias limestone occurs, almost always, in nearly hori- 

 zontal strata, and never attains any great elevation. On the west of 

 Gloucester, at Highnam Park, lias limestone forms a nearly flat pave- 

 ment, resting on red marl, on the summit of a hill about two hundred 

 and fifty feet above the level of the Vale of Severn. From this 

 point to the north-west, there is no bed of lias known in England or 

 Wales ; but it is found in the north-west part of Ireland, and in some 

 of the Hebrides. At Barrow-on-Soar, in Leicestershire, lias rises 

 considerably above the level of the river ; it is in the flattened balls 

 that occur in the Barrow limestone, that the finest specimens of fossil 

 fish are found. The most interesting junction of lias and red marl, 

 that I have observed, occurs in the south side of the Severn at Aust 

 passage, where the red marl may be seen for a considerable distance, 

 supporting the lias, but separated from it by a micaceous bed, filled 

 with broken bones of saurian animals, and other organic remains. 

 Another junction is mentioned Chap. II. p. 20. The lias clay, from 

 its comparative softness, has been more affected by the action of tor- 

 rents and inundations than the strata above or beneath it : hence it is 

 frequently excavated into valleys. Some of the mountain valleys, in 

 the Alps, are cut in lias clay. The lias limestone of the Alps and 

 the Jura, loses its flat and parallel stratification, and is bent and con- 



* Mr John Phillips, in his recent survey of the Yorkshire coast, estimates the 

 average thickness of the lias, comprising the lower, middle, and upper beds, at 

 850 feet, or 283 yards. 



