I. 0. Russell — Glacial Records in the Newark System. 501 



Before examining the evidence, let us endeaver to determine 

 what facts should be looked for, in case glaciers did invade the 

 area in which Newark rocks were being deposited. 



Preservation of Glacial Records. 



All records of glaciation not buried beneath subsequent 

 deposits, would certainly be destroyed by subaerial decay and 

 erosion, during such a lapse of time as has intervened between 

 the Newark period and the present day. Exception to this 

 conclusion may, perhaps, be found in the changes which gla- 

 ciers make in the drainage and topography of a region, but 

 this matter is as yet little understood. Among the direct evi- 

 dences of glaciation which might be preserved for indefinite 

 ages, under suitable conditions, the following may be enume- 

 rated : 



First. Smoothed and striated rock surfaces, if buried beneath 

 fine sediments, might be preserved in their original condition ; 

 or casts of them might be taken, in the same manner that casts 

 of footprints, showing the most delicate markings, have been 

 preserved in great abundance in the Newark rocks themselves. 



Second. Bowlders, smoothed, faceted and striated by glaciers 

 (similar markings are also produced by river ice), might retain 

 their records for indefinite periods, especially if they were im- 

 bedded in fine sediments or cemented by calcareous or other 

 infiltrations.* 



Third. When glaciers enter an estuary or a lake, moraines 

 are deposited in unassorted or but imperfectly arranged, heaps 

 about their extremities. The distance from the shore to which 

 these deposits may be carried depends on the size of the glaciers 

 and on the depth of the water they enter. A shallow estuary or 

 lake could offer but feeble resistance to the advance of glaciers 

 and might have moraines deposited widely over its bottom. 

 On the other hand, glaciers entering a basin in which the water 

 is as deep as the ice streams are thick, would have their advance 

 checked abruptly and the moraines deposited would be con- 

 fined to the borders of the basin ; but scattered bowlders might 

 be carried to great distances on floating ice. Should glaciers 

 plow their way into shallow basins in which fine sediments 

 were being deposited, it is evident that the beds beneath them 

 might be greatly disturbed, while contortions would appear in 

 adjacent strata owing to the unequal distribution of the load 

 imposed on them. 



* Since writing these pages, a paper has appeared by Dr. Haus Reusch, on 

 " Glacial stripe and bowlder-clay in Norwegian Lapponie from a period much 

 older than the last ice-age." Norges geol. undersogelse aarbog for 1891, in which 

 descriptions are given of striated rock surfaces protected by morainal material 

 containing striated and faceted bowlders. These records are thought to be of 

 Carabro-Silurian age. 



