JE. 0. Pickering — Nebula-pho 



until as before stated, in the region of the Laramie Hills, it is 

 compressed into 1,200 feet. From the observations of New- 

 berry, and the later accounts of Gilbert, Powell and Marvine, 

 it is clear that it also shallows toward the south, and the obser- 

 vations of the Carboniferous in California would indicate thin- 



The Archajan body spoken of in western Nevada may or 

 may not have had a continental significance. It would seem, 

 however, from the relations of the Carboniferous in the Blue 

 Mountains of Oregon and Bass' Kange in California, that, if 

 a continental mass, it possessed deep westward bays in which 

 the Paleozoic sediments were deposited. It is, however, prob- 

 able that the Archaean body was only a mountainous region of 

 no very great east and west development, and that the Paleo- 

 zoic sediments were deposited around it to the north and south. 



While as yet no n on -conformity has been observed in the 

 whole series from the base of the Cambrian up, there is in middle 

 Nevada an evidence of shallow water and the accumulation of 

 plant-bearing earthy coal beds in the upper part of the Wahsatch 

 limestone. When the detailed stratigraphy to the south of our 

 field comes to be worked out, it is possible that a local uplift 

 will be found near the close of the deposition of the Wahsatch 

 limestone. But otherwise throughout the whole extent we have 

 no indication of a non-confornaity. On the contrary, there 

 seems to have been a continuous undisturbed deposition varymg 

 between siliceous and calcareous sediments in which the hues 

 of these two types of material have been sharply drawn m a 

 deep oceanic basin over the greater part of the area of Utah and 

 Nevada, while toward the shallow shore in the region of the 

 Rocky Mountains the deposit was more irregularly mixed. 

 Aside from the intimation of a local shallowing at the close of 

 the Wahsatch limestone in western Nevada, the evidences are 

 all of deep-water deposits till near the close of the Upper Coal- 

 measure series, when ripple-marked shales make their appear- 

 ance, and the Permian depositions thereafter seem all to be of a 

 shoal-water character. 



Art. LXVL--.4 Nehula-photometer ; by E. C. Pickeeing. (From 

 a letter to the editors, dated Boston, April 5, 18V6). 



Ak examination of the article in the May number of this Jour- 

 nal on the changes on the Nebula M. 1 7 shows the desirabihtv 

 of accurate photometric measurements of these bodies. 1 wisft 

 therefore to make known the following nebula-photometer in 



