CLIMATES OF GEOLOGIC TIME. 293 



closely to the boulders prevented me from examining more than two or three in the limited time 

 at my disposal. From a similar boulder-rock at Mortensnes, however, which I unfortunately 

 missed seeing, Dr. Reusch describes and figures well-glaciated blocks of dolomite. * * * The 

 form of the intercalated mass of boulder-rock, as well as the fact that fragments of it occur in 

 the base of the overlying strata, indicate that it underwent denudation before it was buried. 



"The boulder-rock rests on a regularly-bedded sandstone of the usual tyj)e, and has been 

 weathered back so as to expose several scjuare yards of the remarkably even surface of that rock. 

 The platform thus exposed is not only smoothed, but conspicuously and characteristically striated. 

 The scratches can be followed in some cases for 2 or 3 yards, not only up to the foot of the little 

 cliff of boulder-rock, but under it, a fact of which I made certain by wedging out some masses of 

 that material and exposing a fresh portion of the platform. * * * The sandstone is traversed 

 by a few irregular joints, the lines due to which, however, on the striated platform bear no resem- 

 blance to glacial groovings. The striae have, beyond question, been cut into that surface indepen- 

 dently of any structure possessed by the rock, and are in all respects characteristic glacial markings. 



"The evidence detailed above seems to leave no room for doubt that we have here an inter- 

 calation of a true glacial till in the Gaisa formation. * * * i accept without hesitation Dr. 

 Reusch's conclusion that the phenomena are due to glacial action, and that they were produced 

 contemporaneously in the Gaisa formation" (1897: 140-43). 



"The Gaisa beds, so far as I saw them, do not suggest the immediate neighbourhood of a 

 mountain-region, for such conglomerates as they contain are neither coarse nor plentiful. The 

 facts tend rather to indicate a temporary deterioration of climate" (145). 



UNDATED PEOTEROZOIC GLACIATION OF CHINA. 



Nan-t'ou formation. — A series of sandy and argillaceous rocks seen only beneath the Cambric 

 limestone cliffs at Nan-t'ou (long. 110° E., lat. 31° N.). The basal strata, Blackwelder states, 

 "consist of arkose sandstone and conglomerate, which are purplish-brown in color below, but 

 gradually become white and purely cjuartzose in the upper strata. Throughout the total thickness 

 of perhaps 150 feet, 45 meters, the texture is coarse and gritty" (1907: 267). 



He says further: 



"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 horizontal. * * * The 

 rocks range in size from sand-grains to blocks 50 to 75 cm. 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, i. e., 

 angles are present, but are smooth and rounded. The flattish surfaces of such slowly weathering 

 rocks as the massive siliceous ferruginous limestone are polished and scratched in various direc- 

 tions, and are identical in aspect with pebbles from the Pleistocene boulder-clays of North America 

 and Europe. The scratched stones were found in numbers firmly fixed in the green tillite, in 

 such a condition as to show that they had never been disturbed nor subjected to surface abrasion 

 since they were imbedded there in early Paleozoic time. 



"The promiscuous arrangement of the pebbles, the heterogeneity of the mass and of its 

 lithologic components, the subangular shapes of the stones and especially their striated surfaces 

 are positive characteristics of glacial till. The evidence of glacial origin is quite as plain as that 

 usually seen in the Pleistocene of the United States or Great Britain. * * * It is highly 

 proliable that these glacial beds on the Yang-tzi are of early Cambrian age" (267-9). 



To this Willis adds: 



"Nan-t'uu tillile. — The Nan-t'ou glacial deposit occurs in longitude 111° east, latitude 31° 

 north, about 200 feet, 60 meters, above sea. It evidently accumulated close to sea-level in 

 early Sinian [= Cambric] time, as it is overlain by marine limestones of that age. At the base 

 the plane of the pre-Sinian unconformity is characteristically developed and covered by a cross- 

 bedded quartzite. which may have been either river deposit or beach. The top of the quartzite is 

 generally covered in the type locality and a cultivated slope interrupts the section for 100 feet, 

 30 meters. Above the terraced fields occur steep banks of tillite, a greenish rock, about as hard as 

 unweathered shale, of irregular hackly fracture, not stratified, and containing pebbles and boulders 

 of various kinds and sizes, many of which are striated. The thickness seen is 120 feet, 36 meters. 



