Terry.] 346 [December 18, 



formation must be regarded as a downward extension of the Potsdam 

 Sandstone. "Whether this assumption be correct or not, is to be de- 

 termined by the import of the latter term. The word "Potsdam," 

 in the earliest geological sense given to it, and as properly understood, 

 primarily refers to the just mentioned sedimentary rocks in the town- 

 ship of Potsdam, and therefore, of course, includes whatever belongs 

 to the said group of strata at that place. It also applies, by legitimate 

 extension, to all rocky beds elsewhere found, of the same specific life- 

 period. Accordingly, to belong to this series of deposits, a formation 

 must either exactly answer in age to the beds at the typical locality 

 in Potsdam, or else be a conformable extension, upward or down- 

 ward, of synchronous rocks — that is, of rocks identical with them in 

 the titne of their deposition. 



How is it, now, with the sedimentary strata before us; what is their 

 relative position? In the first place, the slates underlying the Red 

 Sandstone of Vermont do not conform with it in dip. It is true 

 that this want of agreement iu the inclination of the beds is not great; 

 still it is a clear instance of non-conformity, amply sulficient to indi- 

 cate difference in age between the lower and the upper rocks. The 

 variation referred to maybe seen at Snake Mountain, in Addison 

 County; in Charlotte, Shelhurn, Burlington and Colchester in Chit- 

 tenden County ; also in St. Albans, Swanton, and Ilighgate in 

 Franklin County, as well as in other places. 



A"-ain, there is a lack of conformity in the strike of the sandstone 

 and of the underlying slates. This fact may be observed at the sev- 

 eral localities just mentioned. It is especially apparent to a person 

 surveying the Avhole range, as it stretches from one end of the Cham- 

 plain valley to the other. A glance at the representation given on the 

 Geological Map, published in the "Final Eeport" on the Geology of 

 the State, will enable us, in case Ave make due allowance for differ- 

 ences in names, to estimate this discordance in its true bearing. 

 Startino- from Whitehall, New York, and passing down the valley of 

 the lake, we see that the trend of the sandstone from west of south 

 to east of north, is clearly greater than that of the subjacent forma- 

 tions. Indeed, its western edge passes obhquely across the Black 

 Slates (called, on the map, "Utica" and '"Hudson River") and the 

 Georgia Slates, as may be well observed in the field, at various points- 

 along the line of strike throughout the range. 



Once again, it should be remarked that there is a lack of conform- 

 ty in the organic remains. The fossils which I have found in the 

 two underlying masses of rock are as follows: (1.) in the Black or 

 Swanton Slate, several species of Graptolites, Atops tr'dineatuK (Emm.), 

 and fragments of one, or perhaps of two, closely allied species as yet 

 undescribed; (2.) in the Georgia Slate, one, if not two, undescribed 



