NATURAL HISTORY OF THE DIATOMACE^E. 465 



any one of them might be of great thickness, yet it does not necessarily 

 follow that it had been forming for any great number of years; and 

 geologists and others are not warranted, from observance of this one 

 fact of thickness, in supposing that a great length of time has inter- 

 vened during its deposition. Thus, some years since, I examined one 

 of these lacustrine sedimentary deposits, at a spot near the town of East 

 Stoughton in Massachusetts, which was fully twelve feet thick, but only 

 covered a few feet of surface, which circumstance was due to the occur- 

 rence of a dam across the course of a stream, which arrested its progress 

 and formed a small, deep pond, into which all of the diatomacese, which 

 grew for some considerable distance up stream, drained, and, dying, 

 accumulated as a light grey-colored powder. I have received specimens 

 of similar material from many points in this country, so that about one 

 hundred have been examined. The state of New Hampshire has sup- 

 plied quite a number, and they will be hereafter described, and the 

 forms detected in them illustrated. 



The first recorded discovery of a lacustrine sedimentary deposit of 

 diatomaceas in this country is found in Sillimaris journal, 1839, v l- 

 xxv, p. 1 1 8, in an article " On Fossil Infusoria discovered in Peat-earth 

 at West Point, N. Y., with some notices of American species of Dia- 

 tomae. By J. W. Bailey." Of this I have a small portion given me by 

 Prof. Bailey himself, and, on examination, it is found to have the general 

 characteristics of these deposits; that is to say, it is of a grey color, 

 light in density and very friable, and is made up of the siliceous skele- 

 tons of such species of diatomaceae as grow in small fresh-water lakes, 

 ponds, and marshes. In fact, Prof. Bailey says that this deposit, which 

 was "eight or ten inches thick, and probably several hundred square 

 yards in extent," was discovered "about a foot below the surface of a 

 small peat-bog immediately at the foot of the southern escarpment of 

 the hill on which the celebrated Fort Putnam stands." He considers 

 the remains present in this stratum to be "in a fossil state." And here, 

 perhaps, it is desirable to say something with regard to the use of this 

 term. Its origin would warrant its being applied to anything dug up out 

 of the earth ; and, as Mr. Page remarks in his Handbook of Geological 

 Terms, " hence the earlier geologists spoke of native fossils or minerals, 



and extraneous fossils, or the bodies of plants and animals accidentally 

 VOL. i. 6 1 



