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ironstone nodules are found, from which is made the far- 
famed Mulgrave cement. There are also a quantity of 
fossils found in working this shale, chiefly ammonites, but 
some excellent specimens of the higher vertebrated forms of 
life have been met with. In the Kettleness Alum Works 
some years ago, almost in the same place, two large specimens 
were taken out in a very perfect state : an Ichthyosaurus 
and a Plesiosaurus, measuring from 20 to 30 feet each in 
length. Many other of those immense saurians in an 
imperfect state have been extracted ; they are found at a 
depth of about 65 feet below the surface of the alum rock. 
11. Hard Jet Rock. — This bed of shale is much stronger 
and of a more bituminous and sulphurous nature than the 
aluminous shale ; it is always indicated by a nodulous band 
of inferior limestone, locally known as the top jet dogger. 
The usual mode of getting the jet is by taking the front of 
the cliff away where the line projects, until a seam is found, 
then followed by mining until it runs out. The seams vary 
very much both in length and thickness, in some places only 
a few inches broad, and not more than a quarter of an inch 
in thickness, extending only a few feet ; in other cases, from 
eight to fourteen inches broad, and from one to two inches 
and a half in thickness, extending as far as thirty yards. 
I have frequently observed when the workmen are taking 
the jet out, the centre of the seam was the thickest, thinning 
towards each edge. The jet from this line is superior to any 
other, in consequence of its being easier to work, much 
lighter, and susceptible of a higher polish. Its present 
price in the market is from 5s. to 15s. per lb. The manu- 
facture of jet ornaments appears to have been known in 
Whitby since about 1589 ; however, after that time it had 
gradually declined, for in 1810 there was no consumption of jet 
in the town. I know individuals who have told me when they 
were emploj'ed on the beach collecting and burning sea- weed 
