272 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



and the tillite beneath it is thought to have formed "close to sea-level." The age of 

 these tillites is conceded to be at least as old as the Lower Cambric, but when we note that 

 the tillite changes quickly into the overlying limestone within a few feet of thickness, 

 indicating a probable break in sedimentation between the two series of deposits, and the 

 further fact that the overlying limestones have yielded no fossils, we see that these glacial 

 deposits are as yet unplaced in the geologic column. Professor Iddings restudied these 

 tillites in 1909, and he likewise could find no fossils in the limestone. For the present the 

 tillites are referred to the Proterozoic. "Wliat their distribution has been in China is as 

 yet unknown. (For further detail by WilUs, Blackwelder, and Iddings, see pp. 293-5.) 



Scotland. — In the northwest of Scotland are seen some of the oldest rocks known to the 

 geologists of Europe. The basement formations make up the Lewisian series, comparable 

 to the Laurentian of American geologists. Upon these old gneisses and schists, mainly 

 of igneous origin, reposes unconformably a great pile of dull red sandstones, shales, and 

 conglomerates, referred to as the Torridonian, that Peach states were laid down "under 

 desert or continental conditions" (1912: 50). These attain a thickness of at least 8,000 

 to 14,000 feet, and are in turn overlain unconformably by Lower Cambric strata having 

 the trilobite Olenellus and related genera. The Torridonian was laid down in part upon a 

 mountainous topography of Lewisian domes strikingly suggestive of glacial erosion. 



In western Sutherland and Ross, Geikie states that the observant traveler must be 

 struck by the "extraordinary contour presented by the gneiss. A very slight examination 

 shows that every dome and boss of rock is ice-worn. The smoothed, poUshed, and striated 

 surface left by the ice of the glacial period is everywhere to be recognized. Each hummock 

 of gneiss is a more or less perfect roche moutonnce. Perched blocks are strewn over the 

 ground by thousands. In short, there can hardly be anj^vhere else in Britain a more 

 thoroughly typical piece of glaciation" (1880: 401-3). 



Over this eroded and smoothed ground was formed a coarse reddish breccia with many 

 of the stones decidedly angular and "sometimes stuck on end in the mass." Some blocks 

 are "fully 5 feet long" but none were found to be scratched or striated. The breccia "is 

 quite comparable to moraine-stuff." The material came from a land that lay to the 

 northwest and that has since sunk into the Atlantic. 



Geikie as late as 1903 still stands by these conclusions, for he says: 



"Sometimes, indeed, where the component blocks of the basal Torridonian conglomerates 

 are large and angular, as at Gairlock, they remind the observer of the stones in a moraine or in 

 boulder-clay" (1903: 891). 



"Some of these roches moutonnees in N. W. Scotland may be of Paleozoic age [now classed as 

 Proterozoic] and the Torridonian breccias which cover them have a singularly 'glacial' aspect" 

 (1309). 



"The resemblance of these rocks [Sparagmite] to the Torridonian series of Scotland is re- 

 markably close" (899). 



EARLIEST PROTEROZOIC GLACIATION. 



Canada. — The oldest known tilUte was recently described by Professor Coleman (see 

 figure 89). It occurs at the base of the Lower Huronian in the so-called "slate conglomer- 

 ate," and therefore near the base of the geologic column accessible to geologists. These 

 conglomerates are found "from point to point across all northern Ontario, a distance of 

 nearly 800 miles [now placed at 1,000 miles] and from the north shore of Lake Huron in 

 latitude 46° to Lake Nipigon in latitude 50° [now placed at 750 miles]." "The appearance 

 of these so-called slate or graywacke conglomerates is closely like that of the Dwyka 

 bowlder clays of Africa" (1907: 189). They rest on various formations older than the 

 Huronian, an "undulating surface of low hills and vallej-s, the conglomerate often more or 

 less fining in these valleys" (191). A scratched or polished underground has been found in 

 three places, but as a rule such are not seen because of the unfavorable conditions for their 



