226 Mr. Williamson on the Distribulion of 



lus ofaBelemnites compressus, the solid portion projecting from the nodule, and 

 resting in the shale. The number of these fossils forms a remarkable feature. 



(6.) About the upper part of this deposit occurs Belemnites tubularis, which 

 is almost universally depressed at the smaller extremity, indicating- apparently, 

 that it was thin and delicate. It forms a regular but thin layer, a few inches 

 above or below which it has not been noticed. I have seen it only on the 

 Scar, a little to the south of Whitby, where Belemnites compressus is also 

 found. The top of this deposit is occupied by numbers of Ammonites ele- 

 gans, and Inoceramus dubius, the former being almost always depressed and 

 as thin as paper ; and both it and the Inoceramus are beautifully coated with 

 iron pyrites. 



Throughout the greater part of these shale beds, the fine hard jet, so valu- 

 able for manufacturing ornaments, is found in lenticular seams, from half an 

 inch to three inches thick. It is obtained in quantity only in this deposit, 

 which is called by the workmen the " Jet Seam." 



Towards the middle and upper parts of the seam, large fragments of bi- 

 tuminized, coniferous wood occur, some of them weighing nearly a hundred 

 pounds. 



(c.) This division is by far the most interesting of the three, in its fossil 

 contents. 



Near the lowest part are immense numbers of spherical nodules, all strongly 

 charged with sulphuret of iron. They vary in size from a small nut to six or 

 eight feet in circumference, and often contain Ammonites exarafus, and 

 A. elegans. These nodules are well exposed between Staithes and Runswick. 



A little higher is a bed in which numbers of Nucula ovum occur. This 

 fossil is generally diffused through the upper part of the series, but more par- 

 ticularly in this portion. Associated with it, and sometimes even attached to 

 it, is found Orbicula rejlexa. A very small variety o^ Avicula incequivalvis is 

 met with in the same stratum. 



In all the lower portions of this division, Clhe one from which alum is pro- 

 cured) the remains of Saurians have been found:; and some of the specimens 

 obtained from it ornament the museums of Scarborough, Whitby, and JMr. 

 Witham, of Lartington. 



As yet, I believe only one species of the Teleosaurus and one of Ple- 

 siosaurus have been discovered, but two, and probably more, of Ichthyosau- 

 rus. One of them corresponds with /. tenuirostris, and the other must have 

 l)een an immense species, as I have seen a lower jaw which is seven feet in 

 length, and has many of the teeth preserved, some nearly three inches long. 



The Plesiosaurus varies in size, but from a comparison of detached bones 



