kegory.] PETROGRAPHY OF TUFFS. 129 
re too well silicified to admit water, and hence remain quite fresh at 
he surface. 
The microscope shows the rock to contain quartz and feldspar grains, 
nth fragments of various igneous rocks. The quartz occurs both as 
>artially rounded grains and as secondary tilling of cracks. Feld- 
pars, with orthoclase more common than plagioclase, are found in 
fell-formed crystals, un twinned or with Carlsbad or albite twins, and 
aicroperthite intergrowths. The fragments of volcanic rock include 
udesite and trachyte, with a groundmass of ragged feldspars, often 
arranged in flow structure; fragments, perhaps of formerly glassy mate- 
ial now devitrified, showing feldspar needles in a dark cryptocrystalline 
froundmass, and fragments of vesicular lava with some glass formed 
>y steam blowing back in the vesicles. Besides these evident volcanic 
naterials, which constitute the bulk of the rock, there are also green, 
glassy -looking fragments — macrocrystalline — which may be metamor- 
phosed slates. Most of the components are with angular outline, 
,nd have associated with them chlorite and calcite with beautiful twin 
amellse. 
VOLCANIC CONGLOMERATES OF ASHLAND TOWNSHIP. 
The volcanic sandstones and conglomerate from this locality range 
Tom dense sandstones to coarse varieties, but typically have very 
ngular grains 2 to 3 millimeters in diameter. The rock contains so 
nuch calcite as to resemble a finely brecciated limestone in places, 
tnd to cause it to effervesce freely with' acid. It is blue gray in color, 
weathers to a white gray, and bears close resemblance to the rock 
exposed in Ashland Village, interbedded with the fossiliferous 
imestone. 
Under the microscope the following components are seen: Quartz 
n large, broken, angular to rounded, interlocking grains, and small 
grains filled with inclusions, and feldspar represented by a few crystals 
low altered to calcite and volcanic fragments. The fragments of 
igneous rock comprise most of the material and are largely of andesite, 
md many large and small fragments of vesicular feldspathic lava with 
low structure well developed. There are also areas with a pepper and 
salt appearance, which is taken to represent former glassy material or 
dliceous silt. Some mica is present, and calcite is abundant as a sec- 
3ndary product, and probably also primary as cement. 
VOLCANIC CONGLOMERATES OF NEW SWEDEN TOWNSHIP. 
This rock presents considerable variation in the field, and specimens 
from twelve different localities were collected for comparison. The 
coarsest variety is a dark, unassorted mass of angular and subangular 
fragments of quartz, andesitic and rhyolitic materials, granite, black 
and greenish glassy siliceous slates, and soft black slates, all set in a 
Bull. 165 9 
