206 



that the Mollusks and the Gaiteropods are not specially limited in their langa, 

 many of ^ 'the former certainly recurring again upwards and downwards 

 throughout the entire formation. Further ou it will be seen that the same 

 holds good even more remarkably with regard to the Fish and Siurians. 

 The upper Lias in Somersetshire and Gloucestershire consists for the most 

 part of beds of blue and dark shales, with a subordinate band of limestone 

 towards the lower part. In Yorkshire it presents a somewhat different 

 character, and becomes of considerable economic importance from the abun- 

 dance of sulphate of alumina with which the upper shales are charged, all of 

 which contain iron. The top shale is underlaid by a cement stone bed, and 

 the lower by a bed of jet 30 feet thick. The shales in Gloucestershire and 

 Somerset may contain alum, but I never observed any jet rock or cement 

 stones, and they are of no commercial value, and are only worked for the sake 

 of the marlstone below. The upper Lias is very irregular in its distribution, 

 and, as in Warwickshire, it is often reduced in bulk, and in some cases it is 

 entirely wanting. When it reaches its maximum development it attains a 

 thickness of 200 feet (to 230 feet in Dorset) and upwards. Fossils are 

 generally abundant ; the clays and shales being full of Ammonites, leda, 

 rosiellaria, and other marine shells, and remains of Fish and Saurians. The 

 chief depository of the fossils is, however, the subordinate limestone, which, 

 from the fre«iuent occurrence of fish in Gloucestershire and Somersetshire, 

 has been termed the fish bed. A small species of leptolepU occurs in it not 

 (infrequently in both these counties, and, besides the larger pachycormus 

 and lepidotus associated with it, are some well-preserved Sepia, Crustacea, and 

 Insects, consisting chiefly of Neuroptera and Coleoptera. It was from this 

 stratum that I obtained an entire dragon fly, with wings expanded as if in 

 flight, the finest specimen in my collection. As a rule, however, the insect 

 relics are not so numerous as in the' lower Lias. The limestone containing 

 them is nodular in places, and from one of these I obtained a large and entire 

 specimen of lepidotus. From similar nodules at Ilminster, in Somersetshire, 

 my friend, Mr. C. Moore, procured his fine series of fossil fish in a wonderful 

 state of preservation, and one or two perfect teleosauri. This fish bed is 

 known to occur in Somerset, Dorset, Gloucester, and Northampton, so that 

 it has an extensive range. 



Immediately underlying the upper Lias shales is the Marlstone, the top 

 of the middle lias, a very hard stone of a blue and brown colour, much used 

 for road material, walls, and building purposes, for which in some counties, as 

 at Banbury, in Oxfordshire, it is largely and profitably employed. 



In this part of the series there is a valuable deposit of iron ore, formerly 

 worked, near Gloucester, and now worked in Oxfordshii-e, and more exten- 

 sively in the vale of Cleavland, in Yorkshire. In Gloucestershire, Lincoln- 

 shire, and Yorkshire, it occupies high ranges of hills, and here and there 

 forms outliers, often capped by a thin stratum of upper Lias. In Northamp- 

 tonshire, however, it oscars at a much lower level, the higher ground being 



