628 PKOCEEDINGS OF BOSTON MEETING. 



The "crystals or fragments of inorganic matter" are of quartz. Sometimes the 

 nucleus consists solely of a rounded fragment of a quartz crystal. In other spherules 

 the nucleus is such a fragment surrounded by finely granular quartz ; other nuclei, 

 again, consist entirely of finely granular quartz. The most interesting nuclei are 

 those which contain a secondarily enlarged fragment. These are numerous, some 

 showing a single zone of secondary enlargement, others showing more than one. 

 The first zone of such growth is always cloudy from impurities taken up in process 

 of deposition. If there is a second zone, it is of clear quartz, like the central frag- 

 ment. The enlargements are oriented in the same way as the center and occasion- 

 ally are somewhat indistinctly bounded by crystal planes,^ tliough the tendency is 

 to grade off into granular quartz. The grains of this granular quartz are from 0.04 

 to 0.06 millimeters in diameter. The' large nuclear fragments look like granitic 

 quartz on account of their richness in fluid inclusions, and some of them contain 

 minute acicular crystals of rutile (?). 



No organic remains were observed by the present writer in the section studied 

 by him. 



The principal part of each spherule is made up of a series of very thin colorless 

 and light brown rings deposited concentrically around the nucleus. Between 

 crossed nicols this portion is seen to be composed of minute fibers arranged radially, 

 but the fibers do not extend across from one ring to another, and are, therefore, so 

 short that the whole appears granular instead of fibrous. The optically negative 

 character of this material shows that it is chalcedony. Between this zone and the 

 nucleus a belt of nmch longer chalcedony fibers is occasionally observed. The 

 outer coating of each spherule is a thin shell of colorless chalcedony, which is so 

 fine grained as to be almost aphanitic in texture, when seen in polarized light. 

 This shell is usually sharply defined from the interior of the spherule as well as 

 from the matrix, both in ordinary and in polarized light. It is from 0.04 to 0.06 

 millimeters in thickness, forming from j\ to y\- of the total diameter. The spherules 

 are very symmetrical in shape 'and vary from 1 millimeter to 1.5 millimeters in 

 diameter, though an occasional oblong one is larger. 



Outside the spherules in many instances and concentric with them, though form- 

 ing a part of the matrix, are incomplete, simple or complex fibrous shells of chal- 

 cedony, referred to by Doctor Barbour as " agatized bands." The fibers have their 

 long axes normal to the sphere on which the shell occurs, and they frequently ex- 

 tend through several bands. Some of the cuspidate spaces between the spherules 

 are completely filled with this form of chalcedony, the fibers all being normal to 

 the surface of the nearest sphere ; others have an apparently granular filling, which 

 shows a tendency toward aggregation into ininute spherules, which possess the 

 characteristics of chalcedony and which rarely show any concentric bands. The 

 larger grains in the matrix are quartz. 



The chemical analyses given in Barbour and Torrey's article would indicate that 

 the spherules are almost chemically pure silica, and that all the imi^urities are in 

 the matrix ; but dissolving agents have attacked the former the most vigorously, 

 leaving their outer portions — the minutely fibrous chalcedony — a brown ochreous 

 mass and causing them to drop out of the almost unaffected matrix. 



The rock was evidently made from a clear quartz-sand by the action of alkaline 

 waters depositing silica in the form of chalcedony around the fragments or aggre- 



*0n secondary enlargement of fragments of quartz crystals, see Sorby, Proc. Geol. Soc. London, 

 1880, p. 62; Irving, Fifth Ann. Rep. U. S. Geol. Survey, 1883-'8i, p. 218. 



