436 Prosser — Stratigrwphie Position of Hillsboro Sandstone. 



preserved Halysites or chain-coral, have been discovered in the 

 sandstone. The section at Lilley's Hill shows it in its proper 

 place as crowning the Niagara series, but as it is not covered here 

 by any later formation, the section is not as definite and satisfac- 

 tory as the section of Grady's Hill, or better still, of the Burying 

 Ground Hill, near Samantha. In the first of these instances, the 

 sandstone is interstratified with the Pentamerus and Megalomus 

 beds. In the second, it is directly overlain by 15 feet of Helder- 

 berg [Monroe] limestone, proved to be so by its most characteris- 

 tic fossil."* 



Dr. Orton in his description of "The Geological Scale of 

 Ohio " in 1888 apparently was not absolutely certain that all of 

 the Hillsboro sandstone belonged in the Niagara series, as may 

 be seen from the following quotation : 



"The Hillsboro sandstone is the last element in the Niagara 

 group. It is found in but few localities, and its reference to the 

 Niagara series in its entirety is not beyond question. In High- 

 land county it has a thickness of thirty feet in several sections. 

 It is composed of very pure, even-grained, sharp silicious sand. 

 . . . The Hillsboro sandstone is sometimes built up above all the 

 beds of the upper Niagara limestone, but again, it is, at times, 

 interstratified with the beds of the Guelph division. In the latter 

 case it is itself fossil if erous, but when found alone it seems desti- 

 tute of all traces of life. These sandstones in the limestone 

 formations [Niagara and Monroe] suggest in their peculiarities a 

 common origin. "f 



The same description was repeated by Dr. Orton in 1890+ 

 and in 1893 in the last account which he published of the 

 " Geological Scale and Geological Structure of Ohio."§ 



In 1911 Dr. E. O. Ulrich in the correlation table of the 

 " Neopaleozoic — Silurian and Devonian" in his "Revision of 

 the Paleozoic Systems," gave the Hillsboro sandstone as the 

 basal formation of the Upper Cayugan and equivalent in age 

 to the Sylvania sandstone in the Monroe formation of north- 

 western Ohio. || The writer has found no reference to this 

 formation in the text of Dr. Ulrich's monograph, and does not 

 know the basis for this change in the age of the Hillsboro 

 sandstone. 



Later it appears in the same stratigraphic position in Dr. 

 Bassler's " Silurian Correlation Table " in his " Bibliographic 

 Index of American Ordovician and Silurian Fossils.''^" In this 

 table, however, the Sylvania sandstone and the greater part of 



*Idem, p. 283. 



f Eeport Geological Survey of Ohio, vol. vi, pp. 14, 15. 



\ Idem, 3d Organization, 1st Annual Report, p. 20. 



§Idem, vol. vii, pp. 12, 13. 



|| Bull. Geol. Soc, America, vol. xxii, September, 1911, pi. 28. 



ITU. S. Nat. Mus., Bull. 92, vol. ii, November, 1915, pi. 3. 



