114 JULES MARCOU ON THE TACONIC OF GEORGIA 



In the lenticular mass of limestone, marked on my geological map, between Parker's 

 fai-m and Georgia Centre, Mr. Walcott has been snccessful in finding a few fossils: Lin- 

 yida, Orthisina, Camer(Ma, Agnostus and ConocephaUtes, which he thinks indicates per- 

 haps the Potsdam formation. I regai'd those determinations of Potsdam and fault as 

 merely conjectui-al, and I am convinced that the more eastward Ave go, after leaving 

 Parker's farm, the older are the strata. 



III. Age of the Eed Sa^drock, axd section near Swanton. 



The discordance of sti'atification on the western edge of the red sandrock is so well 

 marked everywhere, and Billings was so positive as to the paleontological age, that I did 

 not hesitate to refer the whole series to the Potsdam sandstone formation. I confess 

 that I ought to have been moi-e careful and moi'c prudent with some parts of them; for 

 I have seen at Swanton red and yellowish calciferous sandrock inclosed in the Georgia 

 slates, and on the road from St. Albans' Bay to Parker's farm I have crossed several 

 ledges of red sandrocks with Georgia slates intercalated in concordance of stratification. 

 But I had so many other questions to attend to, and always thinking that I had full time 

 to make a complete survey, that I passed it over without proper attention. 



The discovery of Mr. Walcott, of the Georgia slates fauna, in some ])arts of the red 

 sandrock, not only at Parker's farm, but also at Highgate Sjjring near Church's farm, 

 shows that I have made a mistake. But are all the red sandrocks of Vermont a part of 

 the Georgia slates, as Mr. Walcott seems to consider them, or some poilion of them 

 only? 



The absence of a geological map from Mr. Walcott's paper leaves us in doubt as to 

 many of his opinions; perhaps if he had tried to put his observations on a detailed map, 

 he would have found difficulties which would have made him hesitate about some of the 

 views presented in his memoir. 



Lithologically there is a great similarity between the red sandrock of Vermont^ and 

 the typical localities of the Potsdam foi-mation at Potsdam, at Keeseville, as well as in 

 Beauharnais county (Canada). Magnesiau limestone interstratified with pure sand- 

 stone or sometimes calcareous sandstone, of gra}*, red and pinkish colors, form the two 

 groups, as well in Vermont as in New York and Canada. The occurrence of similar 

 sequences of beds of the same lithological characters, and so near one another as Keese- 

 ville and Georgia, ai'e certainly jjuzzling and may mislead, if not propeily checked by 

 paleontological and stratigraphical facts. 



Paleontologically, the finding of ConocephaUtes Adamsi in Vermont, so nearly re- 

 lated to Conoce])J>aUtes minuta of Keeseville. was in favor of identification of the two 

 formations. But there is more. I have collected in the section of Swanton, on the 

 ground of Doctor Hall's farm (now Bnllard's farm) in the pinkish-red sandrock, au 

 imperfect glabella of Conoceplialltes minuta; and Mr. Walcott signalizes a Liingulcv' in 



' The red sandrock of Vorinont is generally formed of of Swanton have taken advantage of the varieties of colors 



a limestone containing a little sandy matter, and is almost given by tlnil strnclnre to work largely for the trade sev- 



always raagnesian or doloniitic. It has often a globular eral strata in the vicinity of Swanton and St. Albans, 



structnre, which gives to aonv. of the beds the form of a - '-Second contribution to tlie Cambrian faunas of Nortli 



pudding oreven of a breccia; and the marble manulactiirers .Vmerica," p. ly. 



