woodworth: geological expeditiox to brazil and chile. 81 



result of deposition from floating ice and such distribution can not be 

 depended upon as a basis for discussing ad\ances and recessions of 

 glaciers. It can only be said here that the evidence seen points. to the 

 existence of two horizons on which ice-action directly or indirectly 

 arising from glaciation appears to be demanded. 



It would seem from a comparison of the partial sections visited in 

 t*lie course of this Expedition that the boulder-beds are not persistently 

 parallel formations, that the more typical tillite of one district may 

 pass by gradation or intercalation of deposits into contemporaneous 

 waterworn gravels or sands, now conglomerates and sandstones in 

 another district along the strike of the beds. Thus in the sections 

 along the Jaguaricatu in northeastern Parana, the tillite with large 

 angular blocks surmounts with few inter^■ening feet of beds the white 

 fine sandstone which appears to be a fairly persistent basal and pre- 

 glacial meml^er of the Permian series. In the latitude of Ponta 

 Grossa the tillite appears at a much higher horizon, the apparent 

 place of the Jaguaricatu tillite formation being taken by beds of 

 waterworn pebbles. Again in the gorge of the Iguassu at Serrinha 

 Station, if the beds be truly of Permo-Carbonic age at this horizon, a 

 conglomerate with striated pebbles occupies an inferior position near 

 the base of the series. At Orleans, yet further south, the tillite is 

 replaced in the section by waterworn conglomerates possibly, though 

 not certainly, laid down in the presence of ice in the manner of eskers. 



This alternation from point to point along the present roughly 

 meridional line of exposures, thus described of deposits approximately 

 at the same level in the series, and probably more or less contem- 

 poraneous, finds a parallel in the existing deposits of glacial origin 

 within the glaciated areas of Europe and North America. In travers- 

 ing the glaciated region of the latter area we pass from north to south 

 over belts of till with alternating strips of waterworn gravels and 

 coarse sands and clays. In this particular case the deposits are 

 successively newer in the direction in which the ice retreated, i. e. 

 towards the north. We encounter another mode of deposition of 

 alternating accumulations of ice-laid and water-laid drift, however, in 

 which the likeness to the Brazilian distribution, so far as it is at 

 present known, is equally close. That is where glaciers coming down 

 either as distinct valley glaciers or as outflowing tongues from a 

 central ice-cap reach the coastal plain or sea-floor at the base of a 

 highland region so as to deposit till in the vicinity of the paths by 

 which they reach the low grounds while the intervening areas receive 

 only the waterworn debris. In south Brazil, what seems to be evi- 



