Wadsworth.] 178 [April 16, 



of the copper-bearing rocks. Irving's testimony is directly op- 

 posed to his own views, as also is the testimony of all those who 

 claim that the sandstone near the traps is composed of different 

 material from the detrital rocks of the so-called Keweenaw an 

 series. 



I have, while writing this, before me, under the. microscope, sand 

 from this Torch Lake sandstone which shows the structure of the 

 quartz stated. The bi-pyramidal quartz has since been found by 

 Irving, who however considers that it has been produced by the 

 secondary enlargement of rolled quartz grains (Bull. U. S. Geol. 

 Surv., 1884, No. 8, p. 41.) At the time of my observations Sor- 

 by's Presidential Address, which Irving makes the basis of his 

 studies on the secondary deposition of quartz, had not been pub- 

 lished, or at least been seen by me. I made my observations sim- 

 ply by examining the dry sand in air under a lens and by the lower 

 powers of the microscope. I have never recurred to the subject 

 since except at the time of writing the above paper, when my ex- 

 aminations were made as before, simply to see if I had been mis- 

 taken in observing the bi-pyramidal forms. Now, however, ow- 

 ing to the publication of the Bulletin above referred to by Messrs. 

 Irving and Van Hise, I have prepared mounted sections especially 

 for the purpose of testing the correctness of Irving's supposition. 

 These preparations fully confirm his views as to the secondary 

 origin of the quartz facets deposited on the rolled quartz. I there- 

 fore entirely retract all of my conclusions based on the observed 

 pyramidal forms. In order to ascertain the derivation of the 

 quartz grains, sections were ground and mounted in balsam, so 

 one could see if they internally presented the structure of the 

 quartz of the Copper-bearing felsites or not. None of the bi- 

 pyramidal inclusions were observed (Bull. Mus. Comp. Zool. 1880, 

 vii, 120), but numerous fluidal cavities and in some grains many of 

 the hair-like trichites so commonly seen in the quartz of granites 

 and in many of the conglomerate pebbles of Keweenaw Point were 

 found. The evidence is far from being decisive whether this 

 sandstone is composed entirely of the detritus of the Azoic rocks 

 or in part from the debris of eruptive rocks similar to those in the 

 Keweenaw conglomerates. While the facts only are to be sought, 

 yet I am very much pleased to be able to confirm Professor Irving's 

 observations and to amend my conclusions, for if this sandstone is 



