282 Discovery of Microscopic Organisms. 



rocks of this country, with a view to determine the presence of 

 organisms analogous to those well known to exist in the flints of 

 the Chalk. This research has been rewarded by the discovery of 

 abundant organisms referable to the Desmidiese, besides a few 

 Diatomaceae, numerous spicuia of sponges, and also fragments of 

 the teeth of Gasteropods. Among the Desmids, there is a large 

 variety of forms of Xanthidia supposed to be the Sporangia of 

 Desmids, besides an occasional duplicated Desraid ; also lines of 

 cells, some of which appear to be sparingly branched. The re- 

 searches have been mostly confined to the hornstone of the Cor- 

 niferous limestone ; though extended also to the hornstone from 

 the Black River limestone and that of the sub-Carboniferous 

 limestone of Illinois, both of which contain some organisms. 



The hornstone nodules from the Black River limestone (as 

 well as the Corniferous) have been since examined also by Mr. 

 F. H. Bradley with similar results. 



These observations will be regarded with much interest by geo- 

 logists as well by miscrocopists. They carry back to a very early 

 epoch forms of life which have hitherto been looked upon as be- 

 longing only to a much more recent era in the life of our planet. 



The analogy of these hornstone nodules to the flints of the 

 Chalk is obvious ; and the discoveries here anounced may be re- 

 garded as establishing their similarity in origin. The organisms 

 figured so closely resemble those of the flint that they might be 

 taken for them ; it is difficult in all cases to make out a differ- 

 ence of species. 



The extreme abundance of the hornstone nodules in our pa- 

 laeozoic limestones will render it easy to multiply observations 

 in this new field of research, which presents an interesting addi- 

 tion to the labors of the microscopist. It will be remembered 

 by those who undertake such examinations that the use of turpen- 

 tine renders the chips of chert almost as transparent as glass. — 



To THE Editors, — Having recently been engaged in examining 

 the microscopic structure of hornstone from Palaeozoic rocks, I 

 send you the accompanying sketches of organic forms which I 

 have discovered. They consist of spicules and gemmules of 

 sponge and fragments of sponges ; Desmidiese, several species of 

 Xanthidia, and disks which probably are to be considered as Dia- 

 toms. Hornstone from the corniferous limestone of central and 

 western New York contains the greatest variety of these organic 

 forms. A few specimens have been found in hornstone of the 

 Black River Limestones from Watertown, N. Y. * * * * 



