GEOLOGY. 341 



well .as fragments of woody stems and branches, flattened and converted 

 into lignite, and in some cases filled in all directions with the perforations of 

 a Teredo. 



The material of the Infusorial stratum is generally of a very fine texture, 

 admitting of being bruised between the fingers into an almost impalpa- 

 ble powder, singularly free from gritty particles. Although usually of a 

 light-gray, almost white color, it includes in some localities layers of an 

 ashy tinge, which are, however, not inferior to the rest of the deposit in the 

 abundance of their minute organic forms. It has throughout a tendency to 

 lamination in a horizontal direction, and toward its upper limit this structure 

 is so distinct as to cause it readily to separate in thin crumbly plates. But, 

 of all its mechanical peculiarities, its great lightness is the most characteris- 

 tic. From experiments made many years ago, Prof. Hosiers found that, when 

 pure and quite free from moisture, this material, in its ordinary state of com- 

 pactness, has a weight only one-third as great as an equal bulk of water. 

 The minute siliceous fossils for which this deposit has long been noted, be- 

 long, as is well known, almost entirely to the family of Diatomaccaa, and 

 include a very large proportion of Coscinodiscus and allied forms, whose 

 exquisitely thin plates, lying in parallel positions in the mass, have probably 

 contributed to the laminated structure before referred to. The number of 

 such frustules and other siliceous skeletons in each cubic inch of the pure 

 material can only be reckoned in millions, and a cubic foot would contain a 

 multitude far exceeding in number the entire human population of the 

 globe. 



OX THE SO-CALLED " BIRD-TBACKS " OF THE CONNECTICUT RIVER 



VALLEY. 



The following paper was presented to the American Association for the 

 Promotion of Science, lSr>9, by Roswell Field, Esq., of Turner's Falls, Mass. 



" When fossil foot-prints were first discovered in the sandstones of the Con- 

 necticut Valley, the theory that they were produced by birds was received by 

 most scientific men with great distrust and skepticism. And it was not until 

 after Dr. Edward Hitchcock had spent much time and labor in comparing, 

 describing, and distributing specimens, that the scientific public became sat- 

 isfied that they were the tracks of once living birds. 



" The great and only proof that they are the tracks of birds, is the organi- 

 zation of the foot, and in the number and arrangement of the joints they 

 probably do agree with living types, and the alternate steps of right and 

 left feet. Living in the vicinity of Turner's Falls, the locality that has fur- 

 nished the greatest number, and beyond all comparison the most beautiful 

 specimens of these tracks, my attention was early drawn to this subject, and 

 I think I may safely say, that I have uncovered more foot-prints, and found 

 more new species, than any other person. I have, moreover, seen thousands 

 of tracks which others have not seen, since, from injudicious blasting and 

 carelessness of workmen, many fine specimens have been broken and lost; 

 others, from the shrinkage of the matrix, or the presence of sun-cracks, are 

 worthless for removing from the quarries. I consider that I have thus seen 

 thousands of specimens that others have not seen; and the better acquainted 

 I have become with the subject, the greater have become my doubts as 

 to the ornithoid character of the tracks. I have no new theory to advance; 

 but if I can rightly decipher the impressions, the animals producing them 



29* 



