INTRODUCTION 157 



point, and go over the section together. During the week that elapsed 

 l)efore they readied "Watertown my work substantially completed the sec- 

 tion. Underneath the impure limestones already noted as underlying 

 the Lowville a series of pure limestone Ijeds was found, which contained 

 not only ostracods, but also other fossils in considerable number. Some 

 of these were the same as forms occurring in the Lowville above, but 

 many were not Lowville species. It seemed to me to be a fauna unlike 

 any that I had ever seen elsewhere in the region, to be closely related to 

 the Lowxille fauna, and certainly to have nothing to do with tlie Beek- 

 mantown. It quickly developed also that this apparently new formation 

 rested upon the formation which had been met with during the work of 

 the previous season and which had been regarded as Potsdam-Beekman- 

 town passage beds. Moreover, it was seen that the one formation rested 

 upon the other with marked overlapping unconformity, magnesian lime- 

 stones coming in imder the fossiliferous limestones with steadily increas- 

 ing thickness going westward, while the fossil limestones themselves 

 disappeared to the east. A few localities were found which showed the 

 contact between the two formations, exhibiting a thin basal conglomerate 

 overlaid by calcareous sands and weak, greenish, sandy shales, and these 

 beds seemed to appear as a constant base for the series, and to change 

 horizon because of the overlap of the formtition. It also developed that 

 the underlying formation showed considerable and rather abrupt varia- 

 tions in thickness along the contact line, which could only be interpreted 

 as due to erosion. There was no normal Beekmantown in the section 

 and the unconformity shown seemed the most important and prominent 

 of any 3ret noted within the New York Champlainic. This is not sur- 

 prising when it is considered that the interval comprises the larger part 

 of Beekmantown and Chazy time. 



Here, then, were two formations separated by a prominent unconform- 

 ity, both by erosion and by overlap, the lower closely connected with and 

 grading downward into the Potsdam, the upper showing close relation- 

 ship with the overlying Lowville, though it can not be said that it grades 

 into it. I could not correlate the upper with any New York formation 

 known to me, and it came to mind that it might represent a near-shore 

 edge of the Stones Elver formation of the interior basin. The lower 

 formation neither lithologically nor f aunally was normal Beekmantown ; 

 it was closely affiliated with the Potsdam, seemed like the passage beds 

 between the two formations farther east, required mapping as a litho- 

 logic unit separate from the Potsdam, and hence required a name — at 

 least provisionally, until study of the fossils should more plainly «et forth 

 its relationships ; so I dubbed it the "Theresa" formation, from the 



