188 APPENDIX. 



The matter undissolved by the acid was diffused in water, or Canada balsam, on slips of glass, 

 and covered by thin glass or mica. "When subjected to the microscope, it was found to consist 

 mainly of fragments of plants, too much disintegrated for determination. 



" Among these fragments there occur various bodies of some interest, especially the siliceous 

 shells of several fresh-water species of infusoria, belonging the family Bacillaria. These are not 

 abundant, forming but a small portion of the marl, which also contains quartzose sand. The 

 species are not distinguishable from those which occur in the siliceous deposits now forming in 

 our bogs, except that some of the predominant forms of the recent deposits are rare in this . 

 specimen. 



" In the figures accompanying this paper (vide Plate XV.) are represented the forms observed. 

 They were drawn by the aid of the camera lucida eye-piece attached to one of' Chevalier's 

 horizonto-vertical microscopes. The figures are enlarged two hundred and sixty-eight diameters, 

 and are all drawn to one scale, indicated by Fig. 19, which represent Jj^ of a millimetre mag- 

 nified equally with the sketches. Many of the infusoria exhibit entirely different appearances 

 when their ventral or lateral faces are presented to view. These two positions are given in the 

 figures ; the letter a indicating in each the ventral face, and the letter b the lateral one. Those 

 species which have but little thickness in proportion to their breadth, rarely present their lateral 

 faces to view, except when turned on the side by means of the compressorium. 



" The forms of most frequent occurrence are those represented in Figs. 1, o, 4, and 10. 

 Fig. 1 is a species of Eunotia, not distinguishable from the living E. "Westermanni. There are 

 seven of the internal transverse cells in a length of ^ of a millimetre. Of Fig. 4 only an outline 

 sketch is given in the position b, no specimen being found with its lateral faces sufficiently entire 

 to afford the details. This species has from five to eight transverse striae in jfa of a millimetre. 

 Fig. 6 is a species of Cocconema, with eight stria? in T l^ of a millimetre. Fig. 8 is a species of 

 Gallionella, nearly allied to, if not identical with, G. varians. The form represented in Fig. 11 

 belongs to the genus Gomphonema, and is perhaps G. acuminatum. The species represented 

 in Fig. 10 is often connected by the lateral faces in short chains composed of two, three, or more. 

 At b are represented two individuals thus connected. The form given in Fig. 1 often presents 

 two individuals united in the same manner. The species of Cocconema, Gomphonema, and 

 various other genera, are attached to a pedicel in the living state. This character is lost in the 

 fossil specimens, and it often becomes difficult to determine the genus ; some of the forms, which 

 in the living state are free, bearing a very close resemblance in other respects to the pedicelled 

 species. 



" A few specimens occur of the forms represented in Figs. 2 and 5. Fig. 5 cannot be • 

 distinguished from Pinnularia (Navicula) viridis. It has six strias in T fa of a millimetre. Pin- 

 nularia viridis, Eunotia "Westermanni, and Stauroneis Baileyei, are among the most abundant 



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