108 JULES MARCOU ON THE TACONIC OF GEORGIA 



I had intended. However, I concluded to publish my observations as they were, in order 

 not to lose them, notwithstanding my absence from Caml)ridge — I was then at Salins 

 (Jura) — and the want of a reference to my specimens, and with only a part of my note- 

 books in hand, trusting to my memory more than was prudent. So it is not surprising 

 that I have made some mistakes, and did not give my observations as accurately as they 

 appeared in my note-books, more especially the notes taken in 18G1, which were left in 

 Cambi'idge. 



The important memoir of Mr. Charles D. AValcott, " Second Contribution to the stud- 

 ies on the Cambrian faunas of !N^orth America" (^Bulletin U. S. Geol. Sure, No. 30, 

 Washington, 1886), corrects me in two instances where I have made errors, which were 

 contrary to all of my observations made in 1861, as entered in my note-book. The 

 errors on my part ai'c no less true, and I thank Mr. Walcott foi- his corrections. 



The first is a lenticular mass of calcareous sandstone enclosed in the cliff of Parker's 

 farm, a little north of the quarry. By mistake, I have given a section on page 24 of my 

 memoir, representing a deposit of Potsdam sandstone or red sandrock lying in a sort of 

 depression or hollow upon the Georgia slates. Mr. Walcott has demonstrated that it is 

 a lenticular mass containing the same fossils, Olenellus, Bathynothus, etc., as the Geor- 

 gia slates. He kindly refers to a letter I wrote him, December, 1885, correcting my er- 

 ror and giving him a co]iy of my section as I find it in my note book of 1861. I give it 

 now, Plate 13, fig. 1. The lenticular sandstone is enclosed by folded slates around it 

 except on the top. Its dimensions are: 4:5 feet in length and 20 or 25 feet in thickness. 

 Several loose pieces lie at the foot of the cliff". I did not find fossils. The dip of the 

 strata varies, according to places in this section. At the lenticular mass, the dip is only 

 12°; at the bending of the arch, forming the middle part of the quarry, the slates .and 

 sandstone dip 35° to the east, but at the south and in the depression towards Parker's 

 house, the black slates dip only 10°. 



The second error corrected by Mr. Walcott is more important. In my section, Plate 

 II, fig. 1 (^Bulletin Soc. Geol. France, 1880, ix), from Lake Champlain to Parker's 

 house and the village of Georgia, I have considered the red sandrock, east and west, that 

 is to say, on each side of the "Olenellus zone" of Parker's quarry, as Potsdam sandstone. 

 Mr. Walcott has shown conclusively by direct superpo,sition of the Georgia slates over 

 the red sandrock, and by finding fossils, such as Olenellus Thomj)Soni, Kutorgina, Oho- 

 lella, etc., that at least the first three hundred feet Avest of the Parker quarry belong to 

 a lenticular mass of reddish-pink dolomitic limestone and arenaceous limestone enclosed 

 in the Georgia slates, and consequently ai'e a part of the Georgia formation. 



I must say that such was my first impression and in my field notes of 1861, I have 

 drawn a section similar to the one given by Mr. Walcott. I cannot find in my several 

 note books of 1862-63 and 1873 any justification for the change I made in my first sec- 

 tion, Avhich I now give (Plate 13, fig. 2), only I remember that at one of my last visits, 

 a deep ditch of four or five feet had just been dug for drainage close by the eastern edge 

 of that dolomitic limestone formation, and in such a position in regard to the dipping 

 of the red sandrock that, if the limestone were enclosed in the slates and overlaid by 

 them, the ditch ought to have reached the red sandrock, biit it did not; and, very likely, I 

 concluded that they were Potsdam sandstone, lying in discordance of stratification over 

 the Georgia slates. Besides I did not find any fossils. 



