92 ROCHESTER ACADKMV OF SCIENCE. | J^n. II, 



DEPTH. 'n^eSS\ KORMATKiN. 



Hudson 

 598' and 



Utica. (') 



954' Trenton. 



137' Calciferous (?). 



2006' 



2960' 



3097' 



3' Archean (?).* 

 3100' IJotlom of well. 



Professor Fairchild writes : "No allowance is here made for errors 

 in rneasurement b)^ the drillers. I think that eleven feet should be 

 taken from the Niagara and added to the Medina making the latte^r 

 1 169 feet thick." (Letter of October 6, 1891). 



From the preceding well sections, a general section has been com- 

 piled giving the approximate thickness of the different formations, 

 together with the total thickness from the Olean conglomerate (?) 



(1.) Sample No. ^4, at 1818' is a dark blue argillaceous shale which in lithologic characters 

 resembles the Utica shale. But, the next sample. No. 35 from 1868', is a bluish shale like the Hud- 

 son above. Sample No. 36, at 1912', is undoubtedly Utica and No. 37 from 1928' is likewise a dark 

 blue argillaceous shale. 



(*) [Note.— The following letters to Professor H. L. Fairchild from Professor J. E. Wolff' 

 Instructor in Petrology at Harvard University, concerning the petrographical examination of the 

 samples of rock from the Rochester well, supposed to be Archean, are self explanatory, and this 

 seems to be the most appropriate place fur their insertion. For the original article by Professor 

 Fairchild describing the samples from this well see Vol. I of the Proceedings, pp. 182-186. Ed. 



Ca.miirid(;e, Mass., April 21, 1892. 



Dear Prof. Fairchild : — I have had a number of thin sections prepared of the material you 

 sent me from the Rochester deep well with the following results: 



Sample 62 in slides. The fragments of shale are microscopically composed of small rounded grains 

 of quartz, more angular ones of feldspar, (both orthoclase, plagioclase, inicrocline, and microperthite) 

 and a cement stained yellow by iron hydrate, apparently composed of a micaceous element with some 

 calcite. Some of the fragments are of a fine-grained limestone. 



Sample 63 in slides. Sample in grains effervesces with cold cone. HCl, strongly if warmed. 

 Fragments of fine-grained limestone, often containing round grains of <iuartz of larger size than the 

 calcite grains ; also fragments of loose quartz, part of which have certainly been broken out of the 

 above limestone. There are also fragments of the same fine-grained grit or shale as in 62, very 

 feldspathic. 'I'here is one large fragment of microperthite (intcrgrowth of two feldspars charac- 

 teristic of Laurentian gneisses) and also one fragment of a rather fine-grained gneiss composed of 

 microcline and quartz. The last two fragments are undoubtedly from the Archean gneiss, but of 

 course might have come from pebbles in the basement rock resting on the Archean. Also frag- 

 ments of calcareous quartzite composed of rounded grains of quartz with a calcareous cement. 



Sample 64 is composed of pure quartz grains, ferruginous and masses of limonite. Occasionally a 

 grain of microcline or other feldspar. 



The points that strike me are that in sample 63 the limestone contains frequent large apparently 

 clastic grains of quartz and that the quartzite is also calcareous. This is the character of the Cam- 

 brian (Stockbridge) limestone at Rutland, \t., in proximity tothe underlying Olenellus quartzite. The 

 fragments of feldspar from the Archean and of fragments of gneiss su,ggest close proximity to the 

 Archean at least. That both in this and 64 there should be so little feldspar comparatively makes me 

 doubt whether these come actually from gneiss, the hornblende or miia might be supposed to have 

 floated off, but there ought to be more feldspar. It would look more like a feldspathic quartzite very 

 close to gneiss. * * * * ^■ours very truly, J. E. WOLFF. 



Camhridgk, Mass., May 6, 1892. 



Dear Pkok. Fairchii.ij :— In reply to your letter of April 29th, the sample 63, which I have, efferves- 

 ces gently with cold concentrated HCl, and violently when slightly warmed, showing a dolomitic ten- 

 dency. The microscopic description shows that there are grains of calcareous quartzite. quartz-bearing 

 limestone or dolomite, and fine-grained grit or shale, so that it is a mixture of fragments of three kinds 

 besides the feldspar and gneiss. You are welcome to make any use you can of these microscopic 

 determinations although they do not seem decisive enough to have great weight in the question 

 whether or not the Archean was struck. * * * » Yours very truly, J. E. VSOLFF.] 



