SEDIMENTARY ROCKS 191 



beds on lithological evidence alone. As shown on the table of formations, 

 these limestones and dolomites persist in the northern portion of the belt, 

 from the Devonian down to and including portions at least of the Cam- 

 brian. Going southward, however, these beds give place gradually to the 

 shale series, so that to the south of Tatonduk Kiver only Cambrian and 

 the lower portion of the Ordovician are represented by these beds. To the 

 north on Harrington Creek the limestone-dolomite series extends upward 

 to and including portions of the Devonian and is overlain by Devonian 

 shales. 



These beds in the northern portion of the belt have an aggregate thick- 

 ness of at least 4,000 feet, and possibly much more than this amount, but 

 no section of them was at all closely measured at any one point, it having 

 been found very difficult to do so on account of folding and faulting, and 

 owing also to the fact that the beds are lithologically very similar through- 

 out, and thus include practically no stratigraphical horizon markers. To 

 the south, these beds do not appear to be so thick, but even there they have 

 an aggregate thickness of at least 3,000 feet. 



These rocks are prevailingly white to light gray in color, but occasional 

 beds occur having a dark gray to nearly black or even a pink or reddish 

 appearance. Nearly everywhere, however, on weathered surfaces the dif- 

 ferent members have the peculiar grayish to bluish gray, rough appear- 

 ance characteristic of limestones. The rocks are dominantly crystalline, 

 and in places beds of particularly beautiful marble occur, ranging from 

 pure white through various shades of gray, and even occasional reddish 

 beds were noted. In texture these limestones and dolomites vary from 

 firm, dense dolomites to coarsely crystalline almost pure limestones. They 

 are also characteristically somewhat massive in appearance, due largely 

 to the degree of metamorphism which they have suffered ; but where the 

 bedding planes are discernible the strata are dominantly from 1 to 6 feet 

 in thickness, although much thinner beds, from 1 to 6 inches thick, are 

 locally characteristic of the series. Beds of limestone having an oolitic 

 structure also occur to the south of Tatonduk Eiver and elsewhere, the 

 oolitic grains being generally about one-tenth of an inch or less in diam- 

 eter. In a few places grayish, yellowish to nearly black shales are inter- 

 calated with these limestone-dolomite beds, and at one point on the west- 

 ern side of Mount Slipper over 200 feet of thinly bedded shales occur, 

 with dolomites above and below them. Shales, however, are of very minor 

 importance quantitively in this terrane. The entire series is very siliceous, 

 and toward the south the beds contain a great amount of translucent to 

 semi-translucent chalcedonic quartz or chert, which in places considerably 

 exceeds the limestone and dolomites in amount. This chert has in places 



