424 PROCEEDINGS OF THE ACADEMY OF [1898. 



and Stauroneis Phoenicenteron can be considered as distinctive of 

 later deposits. 



" In general, therefore, it may be said that the deposit can be con- 

 sidered as a mixture of Miocene and later deposits, though the lat- 

 ter need not necessarily have been so very recent." 



From an examination of the above list of diatoms the present 

 author would classify them as follows : Six forms characteristically 

 Miocene, 19 forms that have survived from Miocene to present time 

 and are now living, and 4 either Pliocene or Pleistocene, or both, 

 and also now living. These 4 are the same as those noted above by 

 C. S. Boyer as distinctive of deposits later than Miocene. 



If the 19 survivals belong to present time, there are 23 that may 

 be considered recent, or comparatively so. Respecting the ex- 

 clusively Miocene forms it is probable that these have been brought 

 down in post-Miocene times by the James River in its passage over 

 the original beds from Richmond southeastward. It is probable 

 also that some of the individuals of perhaps each of the 19 species 

 having the more cosmopolitan range were also similarly introduced. 

 We are confirmed in this view by the occurrence among the char- 

 acteristic Miocene diatoms of Actinoptychus Heliopelta, a form which 

 the writer has frequently found heretofore both in outcrops and in 

 well borings, but always at or below the base of the great 300 to 

 400 feet Miocene diatomaceous clay bed of the Atlantic Coastal 

 Plain. In Maryland it occurs at the base of this bed in well bor- 

 ings at Crisfield and in outcrops at and near Nottingham on the 

 Patuxent River. In Virginia it has been found in outcrops at 

 Petersburg and Bermuda Hundred. In New Jersey, owing proba- 

 bly to a thickening of the basal beds of the Miocene, it occurs some 

 distance below the main diatom bed. It has thus been found in out- 

 crops near Shiloh and in well borings at Asbury Park and Wild- 

 wood. At the latter place it was found in a thin seam of clay about 

 250 feet below the bottom of the great diatom bed. In each instance 

 just cited its position is at or very near the base of the Miocene, 

 either resting directly upon or only a short distance above green- 

 sands of Eocene Age. Many other borings have been made in New 

 Jersey through or nearly through these beds, from which the writer 

 has had complete series of specimens every 10 to 20 feet apart, all 

 of which he has examined, but in none of them has he ever found A. 

 Heliopelta stratigraphically higher than near the base of the Mio- 

 cene. Now the diatom bed outcropping at Richmond, Petersburg 



