NATURAL SCIENCES OF PHILADELPHIA. i 



On extreme and exceptional variation of DIATOMS, in some White Mountain 



localities, &c. 



BY F. W. LEWIS, M. D. 



In my notice of some new and singular intermediate forms of Diatomaceie 

 from the Saco headwaters, in the Proceedings of the Academy for December. 

 1863, I advanced a theory based ou the comparative absence of Synedra and 

 Nitzschia in the sub-peat of this country, that these curious species were trans- 

 ilionary or comprehensive types conducting from Surirella and allied genera, to- 

 wards the more modern Synedra and Nitzschia ; and that their continuance as 

 living organisms probably depended on exceptional conditions of soil and 

 water, more or less limited in their influence, peculiar to the Saco and similar 

 localities. 



Since the publication of that paper I have received from my friend, Mr. C. 

 Stodder, of Boston, a very interesting lot of slides containing all of these 

 anomalous species, prepared by himself and Mr. R. C. Greenleaf, of Boston, 

 from gatherings at various points along the White Mountain range. 



His localities are as follows : 



(1.) " Brook near the Flume," (Franconia Notch) thirty miles from the 

 Saco pond, and near the western outlet of the valley; contains Surirella 

 Baileyi, S. intermedia, Actinella punctata, Eunotia incisa. 



(2.) " Lafayette Mountain Lake," not many miles distant from the preceding- 

 This lake is at a considerable elevation ; a still sheet of water ; contains Su- 

 rirella intermedia, Actinella punctata, Eunotia incisa, Synedra hemicyclus. 



(3.) "Brook near Bethlehem," on the S. E. side of the Crawford Notch 

 (Saco) about 15 miles distant, also in the valley ; contains Surirella intermedia, 

 S. anceps, S. delicatissima, S. Baileyi, Synedra hemicyclus. 



(4.) " Maurans Lake," on the Cannon Mountain, near Franconia; contains 

 Surirella Baileyi, S. anceps, S. delicatissima, Actinella punctata, Synedra hemicyclus. 



Of this locality Mr. S. writes, " This Lake is on the Cannon Mountain at a 

 high level rarely visited by travellers. The gathering is surface water." 



(5.) " Bemis Pond," not many miles from the Saco spring, is a small Lake. 

 The gathering, according to Mr. S., is " a peculiar sub-aqueous deposit" form- 

 ing the bottom of the pond, " about six feet thick, and composed of nearly pure 

 diatoms." The contained species are Surirella Baileyi, S. intermedia, S. anceps, 

 Eunotia incisa. 



Mr. Stodder adds, " that in his opinion the only explanation of the origin 

 of this and other similar deposits is afforded on the supposition that these 

 diatoms were originally carried out into the still waters of the lake by small 

 streams, and there deposited," an explanation not altogether satisfactory, as 

 most of the species are still-water forms : Navicula rhomboides, N. firma, N. 

 major, Eunotia robicsta," c, usually found in ponds and boggy pools. 



Similar deposits, not containing any of the transitionary species, occur at 

 other localities in New England. One of the most remarkable, ten feet in 

 thickness, is at Randolph, Massachusetts, another at Bristol, N. H. 



Mr. S. thinks, also, that these beds have been deposited at varying periods 

 since the glacial period. 



(6.) "Echo Lake" (Franconia Notch,) a remarkably beautiful pond lying 

 in. the very gorge of the Notch ; contains Surirella intermedia, Synedra hemicy- 

 clus, Eunotia incisa, and curious varieties of Navicula serians and Odontidium 

 tabellaria, hereafter to be noticed. 



(7.) " Gibbs Falls," a short distance from the Saco springs to the west, 

 contains Surirella intermedia, S. delicatissima, Actinella punctata, Eunotia incisa, 

 along with recent species. 



(8.) " Milldam at Gorham," on the Glen side of Mount Washington, con- 



1865.] 



