136 S. W. Ford—Distribution of the Fossiis in the 
thirteen to Nos. 2, 3 and 4; fifteen to Nos. 2 and 8; while five 
are found in all four. No. 1 does not present as good facilities 
for examination as the others, and has yielded but five species; 
but when further studied it will, I have no doubt, furnish a 
larger number. Enough evidence has, however, I think, been 
obtained and here presented to prove that the limestones in 
question, with their associated beds, all belong to a single great 
series of strata. That some repetitions occur in this series I 
have but little question; but I have been unable, thus far, to 
identify with certainty the rocks of any of the exposures exam- 
ined with those of other exposures situated either to the east or 
the west of them. The thickness of this series remains still 
undecided. Ido not conceive that limestone No. 4 forms the 
eastern limit of this series: on the contrary, there is much to 
lead me to suspect that the formation has a rather wide spread 
beyond ; but as the beds to the east of this band that I have 
examined have, up to this time, proved barren of fossils, I have 
made the section to terminate with it. 
his series I consider for the present to occupy a lower geo- 
logical horizon than the typical Potsdam sandstone of the New 
York survey; and to be of nearly if not exactly the same-age 
with the Olenellus or Georgia slates of Vermont, and the Olenellus 
limestones on the north shore of the Straits of Belle Isle, deter- 
mined by Mr. Billings. It may yet prove to be a trifle more 
ancient or more recent than the above named strata, but there 
can, I believe, at any rate be no great difference between them 
in this respect. The fauna of this series is wholly distinct spe- 
cifically from that of the Upper Potsdam of Wisconsin and the 
true Potsdam of New York, as well as from that of the more 
