begoky.] VOLCANIC CONGLOMERATES. 131 
aining a large disk of some shaly material. They are fossiliferous, and 
it times the fossils occur as the center of balls an inch or more in 
liameter which are composed of material similar to the general rock 
bass, but which maintain their individuality and in v. I speci- 
nens drop out of the rock as spheres, or are easily removed with the 
lammer. 
Microscopically this rock shows no peculiarities which distinguish 
t from the types described above, but consists of quartz grains, feld- 
par crystals, fragments of igneous rock of rhyolitic, trachytic, and 
indesitic facie-, with practically no fragments of sedimentary rock-. 
rhe cement is of the same material as the grains, and is usually dusty 
aid of dark color. 
VOLCANIC CONGLOMERATES <>F MADAWASKA LAKE. 
The volcanic conglomerates of Madawaska Lake appear in the hand 
pecimen as a dark-gray rock of rather fine grain, which on weather- 
nff forms an ashv-ffrav outer zone. Round or oval ballsas large - __- 
form a prominent lield character, and are found abundantly embedded 
n the sandstones. They maintain their individuality through all stal - 
)f weathering, and can be seen firmly set in the fresh rock, or partly 
oosened and resting in sockets, or as detached spheres along the lake 
ihore (see PL IX. B). These balls are of different material from 
he sandstone, and when broken open are found to contain no foss 
md to show no concretionary structure. 
The microscope show- the sandstone to be composed of angular and 
•ounded grains of quartz, abundant feldspars, often striated, and many 
'ragments of rhyolitic and andesitic lavas. The slide prepared from 
m embedded sphere showed but few quartz and feldspar fragment-. 
Diit instead was seen to be practically composed of fragments of a basic 
ava and augite crystal-. The cement is of fine material of similar 
lature with considerable calcite added. It seems evident from this 
lissimilarity of composition that the embedded ball is a worn fragment 
)f some tine-grained volcanic conglomerate already in existence at the 
ime the Madawaska volcanic conglomerate was forming 
SANDSTONES AND CONGLOMERATES. 
By referring to the table of classification given at the beginning 
ihis chapter, it will be -ecu that sandstones and conglomerates include 
ill the rock- of sandstone habit whose principal component i- quartz. 
According to the amount and character of the other components, five 
iivisions are made, as seen in the table referred to. These divisions 
ire arbitrarily made for the most part, and it i- possible to supply the 
ransition form.-. It i- also true that no -harp line can be drawn 
between the volcanic conglomerates and the sandstones composed 
