2/0 JURASSIC. 



Ochre has been obtained from the cherty beds of Lias, near East Harptree. Iron- 

 pyrites was formerly collected at Black Ven, Lyme Regis, and Charmouth, for 

 the manufacture of sulphuric acid. Spontaneous combustion, due to the decom- 

 position of iron-pyrites, or Marcasite, has sometimes taken place in the cliffs near 

 Charmouth. Thus it is recorded that in August, 1751, after very hot weather 

 followed by rain, the Lias cliffs at one spot began to smoke, and soon afterwards 

 to burn with a visible flame. 



The Lower Lias limestones are much quarried for building- and paving-purposes, 

 and to be burnt for lime ; in many instances the separate beds have each a local 

 name, known to the quarrymen. The quarries of Street and Keinton Mandefield, 

 in Somersetshire, yield very large slabs, from six to twelve feet square. The 

 Thurlbeer Lias and Knap Stone are locally known near Taunton. 



The cement-stones at the base of the Lias at Barrow-on-Soar have been largely 

 worked for the manufacture of hydraulic cement. The Limestone Beds at Lyme 

 Regis and Aberthaw are similarly noted. 



The ' Ammonite Marble ' found at Marston near Yeovil is composed of A. 

 plaitkosta, and A. ohtusus (the young forms of which are sometimes known as 

 A. Smithi). This stone was discovered in 1778 in the opening of a marl pit ;i 

 and I am informed by Mr. A. Gillett that a large and apparently nodular mass of 

 this stone was obtained at Marston when a well was sunk early in the present 

 century, about the year 1815 ; and this mass, weighing a ton or more, has supplied 

 most of the specimens known from this locality. 



The Lower Lias Clays are often used for brick- and tile-making. Some of the 

 beds are very bituminous, and near Chard and Axminster they have, early in the 

 present century, led to fruitless trials for coal. Similar trials have been made in 

 Lincolnshire, Leicestershire, Shropshire, in Needwood Forest, and Cumberland. 

 Lignite occurs in the upper part of the Lower Lias on the Dorsetshire coast. 



The soil is loamy and brashy, and often of a rich brown colour. Corn, oats, 

 man'Tel-wurzel. turnips, cabbages, and, in places, beans and teazles are cultivated. 

 In niany places the soil is very heavy, where the higher beds come to the surface, 

 as in the vale of Marshwood in Dorset, and the vale of Ilchester in Somerset. 



The ground is generally flat or gently undulating, forming vales, with an escarp- 

 ment at the junction with the Rha;tic beds and Lias limestones, overlooking the 

 vales of Red Marl. 



The Lower Lias is not generally a water-bearing stratum, but holds up or 

 throws out water when porous beds rest above it. 



The pasture lands on the clays furnish material in the vales of Gloucester and 

 Berkeley for the celebrated 'double Gloucester' cheese, and near Melton Mowbray 

 and Leicester for the ' Stilton.' Cheddar cheese may be said to be the product of 

 the pasturages on the Liassic Clays, Red Marl and Alluvium of Somersetshire. 



Middle Lias. 



The Middle Lias, or INIarlstone as it was termed by William 

 Smith, consists generally of two members. The upper 'Brown 

 rock' or 'Rock bed' ( = Marlstone proper) comprises tough iron- 

 shot argillaceous limestones or marlstones ; the lower member 

 includes micaceous sands, marls, and clays, with occasional 

 nodular limestones. The Middle Lias varies in thickness from 

 one or two feet to over three hundred feet. It has been divided 

 into two zones, as follows : — 



2. Zov^t oi Ammonites {Amalthms) spinatus. 



I. „ „ ,, ,, margaritatus. 



1 W. G. Maton, Observations on the Western Counties, vol. ii. p. 21 ; see also 

 Sowerby, Mineral Conchology, vol. i. p. 167, and Tab. 73 and 406. 



