PARTING QUARTZITE SERIES. 13 
from calcareous sediments; that these beds were subsequently altered to 
dolomite by the magnesium salts of a great evaporating shallow inland 
sea; and that this alteration was accompanied by the production of the 
crystalline structure now characteristic of the rock. 
PARTING QUARTZITE SERIES. 
Above the Silurian dolomite comes a series of thin beds which from 
their persistence and peculiar characteristics are extremely valuable in 
determining stratigraphical questions, for they form a marked and unmis- 
takable dividing zone between the dolomites of the Silurian and the upper 
dolomites, which are almost identical in structure and appearance with 
those of the Silurian, but which are of Carboniferous age. 
Deseription—QOn the top of Hast Aspen Mountain, overlooking the town 
of Aspen, a section of the Parting Quartzite, which was here exposed on 
the face of a cliff for its full thickness, was carefully observed and meas- 
ured. The section is as follows from below upward: 
Section of Parting Quartzite exposed on Hast Aspen Mountain. 
1. Hard, dark-blue Silurian dolomite, passing upward into very thin bedded or shaly 
lisht-eray dolomitess--— =) 2222226222. eee eee a) yee See ee et ee en GRIN GOES: 
2. Greenish-gray sandstone, made up of quartz grains of varying size in a dolomitic 
MA YHEE e 5 enna gob oaaoe Ses aesos BE Sao ane Seae te esetae Sa ee ence rot as Hes a aemeesee 2 feet. 
3. Hard, dark-blue dolomite, like that first mentioned_-_-_-__--....._--..-.-.-------------- 2 feet 
4, Hard, white quartzite, weathering reddish _____.__---_-____-___-_. Be eee eee eee 1 foot. 
OMe Olommibicysamad stone wlio yN|O sic) sa eres ee eee eg ee me ae en a ae 1 foot. 
6. Thin-bedded, gray dolomite shales, like No. 1- I Sone ears en Bf esa eee pt OmMLeO Ls 
Above this, in ascending order, one passing pamennat maedineiliy oO ihe ion come— 
. Fine-grained limestone or dolomite, very much like No. 2 and No. 5, with many quartz 
erains, andioccasional thin)seams of Shales=== 2255.2 5.2 sass 52s oe =n ns eee neo eee 3 feet. 
8. Thin-bedded lime or dolomite shales, light green when fagalh. sraniinaniys yellowish- 
brown, and, when looked at from a little distance, having a general maroon color. 
This color is due to a rich dark-brown staining, which is nearly solid at the bottom 
of the bed; near the top, however, it is in bunches, and is made up of curiously 
~ 
CUHUPVAINES, THANE, COMES MTG THOS = 5 oes sessonsas Lal Hetenages Geedsdesesseeulssee 4 feet. 
9. Fine-grained, light-brown dolomite, with smooth, conchoidal fracture; contains many 
quartz grains, and is a transitional type between No. 8 and No. 10_._______. About 14 feet, 
10. Hard and compact dolomite, light gray in color; from its uniform aphanitic struc- 
ture and regular conchoidal fracture, as well as from its delicate coloring, this 
rock is one of the most characteristic of the series. It has been called in the field 
‘lithographic stone,” from its having a very close resemblance to the peculiar 
limestone which is used commercially for lithographic purposes____ __.____._..__. 8 feet. 
Light-colored, fine-grained dolomites, resembling those of No. 10, but becoming thin- 
beddedvandishalyit 3 522 ani cseet eect Se ee ecu see ase e sec ices Senos ceeean Mlesteebs 
11 
