FORMS. 243 



PLATE X. Nos. 1 and 2 are rounded, elongated, irregular masses. All the other numbers on this plate 

 are examples of rings, either complete or interrupted. Some of them consist of several rings united, as if 

 several cords or ropes of plastic matter were bound together. The largest of these rings is eleven inches in 

 diameter, and this, like some of the others, is nearly a perfect sphere. They are, perhaps, the most remark- 

 able of all the forms of claystones, and are found in Rutland. 



PLATE XI. No. I, flat and thin, with a single concentric belt on the margin. 



No. 2 and 7 are flattened, but made up of several plates which look as if they had been formed by drop- 

 ping successive portions of plastic matter upon the same spot. 



In Nos. 3 and 4 the plastic matter seems to have mantled around the specimen in successive folds, the 

 outer coats not always covering the inner ones throughout. 



Nos. 5 and 8 are flat, with numerous small, often irregular plates, spread over the surface. 



No. 6 shows two flattened circular plates with a connecting belt. 



No. 9 consists of a thin plate of concretionary matter, covered over with numerous often compressed 

 funnels, the narrow openings in which always passes through the plate. These curious forms will be more 

 particularly described further on. 



The sphere, which occurs in Sharon, Pittsford, Ryegate, &c., as already remarked, 

 is the most perfect form of a concretion. But it is one of the rarest forms among 

 the claystones, probably because it is unusual in such a deposit as clay, to have 

 all the essential circumstances present for its production. It becomes an interesting 

 question whether all the other forms can result from modifications of the 'sphere? The 

 numerous forms which were described and figured in a report on the geology of 

 Massachusetts, twenty years ago, we then thought might be derived from the spher- 

 ical, by supposing obstructions to the concreting force, in various directions. Thus, 

 suppose a nucleus or attracting center (it may be a fish, a shell, a pebble or grain 

 of sand) to be established, and the clay permeated by water, to be perfectly uniform 

 throughout, a sphere would result. But if the particles move more freely on two oppo- 

 site sides, than on the others, a prolate spheroid would result. Or if less freely on these 

 sides than the others, an oblate spheroid would be formed. If the particles move freely 

 only in the direction of the lamination, a circular plate would result. Some such are 

 more than five inches across, and not more than a quarter of an inch thick. Sometimes 

 they are annular; that is, are made up of two, three or more, connected flattened rings, 

 of slightly unequal thickness ; as at the Norwich locality. This is difficult to explain. 

 Nearly as difficult is the further fact, that a part of one or more of the outer rings is some- 

 times wanting, so much of it, in some cases, that only a single ear or handle remains, 

 and sometimes a part of the ring is removed on opposite sides. 



Such flattened plates, made up of successive rings, have been called annulated. Some- 

 times such plates, not annulated, are drawn to an edge on their circumference, and are 

 then called lenticular, as they really are ; but by what modification of the formative force, 

 we cannot say. 



Again, it is easy to conceive how the process that forms the prolate spheroid might be 

 continued till a cylinder was pruduced, longer or shorter, according to circumstances. 

 Such cylindrical forms are not unfrequent : sometimes 6 or 8 inches long and half an inch 

 wide. We have seen a few two and a half feet long and an inch wide, in the banks 

 of Connecticut River, in Massachusetts, though a good deal flattened. 



