STRATIGRAPHY OF THE MIDDLE YANG-TZI PROVINCE. 267 
PALEOZOIC. 
The Paleozoic era is represented by a thick sequence of sediments 
of marine origin, beneath which we observed glacial till at one locality. 
With the exception of the Silurian (Upper) and the Devonian and Lower 
Carboniferous, all of the periods from Cambrian to Upper Carboniferous 
are known by fossils. The most prominent features of the Paleozoic are 
two thick formations of massive limestone, one of them belonging to the 
Cambro-Ordovician and the other to the Upper Carboniferous period. 
These are associated with other formations which are largely argillaceous 
or sandy in composition. Igneous rocks of later age than the basal 
complex were not seen at any point in the Yang-tzi valley or along its 
tributary, the Ta-ning-ho, although they are abundant in the valley of 
the Han, not far to the north. 
NAN-TOU FORMATION. 
Basal quartzite and glacial tillite.*—Under this name are grouped the 
sandy and argillaceous rocks which underlie the first of the great lime- 
stones. They are exposed in the gentle slope beneath the cliffs at Nan- 
t’ou; we can not say whether they occur elsewhere or generally, as we 
had no other opportunity to follow their horizon, and their character is 
such as to make it probable that they may be local deposits. 
As stated above, the basal strata consist of arkose sandstone and 
conglomerate, which are purplish-brown in color below, but gradually 
become white and purely quartzose in the upper strata. Throughout the 
total thickness of perhaps 150 feet, 45 meters, the texture is coarse and 
gritty. 
The upper member of the formation is distinct from the sandstone, 
but we did not see the contact and do not know the exact relations. 
The next outcrops above the sandstone occur 100 feet, 30 meters, 
up the slope, and expose about 120 feet, 35 meters, of hard massive boulder- 
clay or tillite, which is neither fissile nor stratified. It is a greenish 
gritty clay-rock of hackly fracture, in which lie irregular stones of various 
sizes and kinds, with their long axes at random angles with the hori- 
zontal. The rocks represented are gray granite, brown-rhyolite-porphyry, 
mica-schist, massive green slate, earthy gray limestones, quartz, and 
chert. The stones range in size from sand-grains to blocks 50 to 75 
centimeters in length, and there is no suggestion of the assortment of 
the individual sizes. Coarse and fine particles lie indiscriminately mingled 
and chaotic in their arrangement. The forms of the majority of the stones 
are subangular, 7. e., angles are present, but are smooth and rounded. 
The flattish surfaces of such slowly weathering rocks as the massive 
*Tillite, a term recently proposed for consolidated till, 
