Bragdon Formation in N. IV. California. — Ilcrshcy. 253 
preaching Delta from the south. Mr. Diller has found that the 
Hmestone pebbles contain Devonian fossils referable to the 
horizon represented near Kennett.* Apparently they have not 
traveled far from the parent ledges. On the western slope of 
Trinity mountain, limestone pebbles are absent or sufficiently 
rare to have escaped notice. 
Supposing the shore-line to have been a short distance east 
of the site of the Sacramento river near Delta, the conglomer- 
ates occurring near Trinity river, not at the base, but in the body 
of the shales, may have been carried by current action fifteen 
miles or more from the coast. Beyond that the conglomerates 
thin and wedge out or are reduced to coarse sandstones. 
Sandstones, silicified into quartzyte, occur plentifully in 
Trinity mountain. Some layers appear to be composed prin- 
cipally of fine chert grains, but others (gray in color, yellowish 
on outcrop) resemble, somewhat, fine waterlaid tuffs. How- 
ever, I am unable to say that there is any volcanic material in 
these layers. Near the summit of Trinity mountain, south of 
Deadwood, I have observed thin-bedded sandstones which were 
rather friable and not much altered. The hard blue-gray 
quartzytes outcrop readily and the soil is largely covered by 
their debris. 
Roughly estimating from memory, I should say that nearly 
one-third of the formation is sandstone (or quartzyte) and con- 
glomerate and the remainder shale. 
The maximum thickness I have been estimating at 2000 
feet. Under some of the peaks of Trinity mountain, the form- 
ation has a vertical range of 3000 or 4000 feet, but I have al- 
ways made an allowance for an exaggeration of the apparent 
thickness of the series by folding and faulting. The highest 
peaks of this region, if not igneous material, are Bragdon strata 
and probably the original surface is everywhere gone. 
There is a total absence, in this Bragdon area, of limestone 
and of chert, except as fragments in the conglomerates already 
mentioned. In this respect the series contrasts strongly with all 
the Paleozoic formations. The soil over the Devonian and to a 
slighter extent over the Carboniferous rocks abounds in chert 
fragments which are continually evident to the field geologist, 
but he finds no trace of chert over the Bragdon shales, except 
• Amer.Jour. Set'., vol. xv, May, 1903, p. 352. 
