122 PHILOSOPHICAL TRANSACTIONS. [aNNO iS/S. 



the real cracks as of a stone or glass. Again^ such stones as consist of many 

 vertebrae or joints, are many of them strangely distorted; sometimes two, three, 

 or more of the joints in a piece are dislocated and out of their places; and some- 

 times a whole series of them. Others seem twisted like a cord. Lastly, some 

 have their joints regular, but stuffed with a foreign matter, as when bricks are 

 laid in mortar. 



There is great variety as to the thickness of the trochitae or single joints : 

 some are so thin, that they are scarcely the 24th part of an inch; others are a 

 full quarter of an inch thick; of these latter I only found at Stock: there are 

 joints of all measures between these two extremes ; but they are mostly of an 

 equal thickness in one and the same piece : and there are slender and small 

 entrochi, which have as thick joints, as the largest and fairest pieces. — There 

 is also some difference in the seams of the joints : some are but apparently 

 jointed; which appears by this, that if they be eaten down a while in distilled 

 vinegar, the seeming sutures will vanish as in sorhe I had out of Staffordshire, 

 from about Beresford on the Dove : • others, and all here at Braughton and Stock, 

 are really jointed, and the sutures indented ; which indentures being from the 

 terminating of the rays, they are larger, according to the difference of the rays; 

 but even, equal and regular. 



Generally the utmost circle of each joint is fiat and smooth ; yet are there 

 many other differences to be noted as to that part : very probably because they 

 are parts or pieces of different species of rock plants. 



The Explanation of the Figures above described. See pi. 5 . 



1. A trochites or single joint, with very fine and small rays. — 2. A trochites or 

 single joint, with the pith bored through like cinquefoil. — 3. A trochites or 

 single joint, of an oval figure, the rays scarcely apparent, and a very small point 

 in the place of the pith. — 4. A single joint of two of a middle size, with the 

 pith very large. — 5. A pack of single joints dislocated, and yet adhering in their 

 natural order. — 6. A very long entrochos, or a piece of many smooth joints, 

 with the branches broken of. — 7* An entrochos with smooth joints not branch- 

 ed. — 8. The largest entrochos I have yet seen, with stumps of branches. — g. A 

 smooth entrochos with very thin and numerous joints. — 10. The deepest jointed 

 entrochos, except the oval one in fig. 3. — 11. An entrochos with very many 

 disorderly knots in each joint. — 12. An entrochos with only one single circle of 

 knots in the middle of each joint. — 13. An entrochos with three circles of knots. 

 — 14. A smooth entrochos, with a large and much raised edge in the middle of 

 each joint. — 13. Alternate joints round or blunt. — 16. A double edg^ in the 



