94 NEW YORK STATE MUSEUM 



changed so niiich. The Precambric rocks in New York cover about 

 11,800 square miles, or about one- fourth of the dry land. In 

 Sweden the proportion is far larger, perhaps nearly nine-tenths. 

 Since one-twelfth of Sweden is covered by lakes the areas com- 

 pared are therefore nearly in the ratio of 4 to 50. 



The older Paleozoic section in Sweden is not so thick as in New 

 York, yet its exposures are very widespread. The relicts left by 

 erosion and spread as they are in scattered areas throughout the 

 kingdom, indicate the very general presence of these strata at one 

 time over all of its extent. The island of Gothland in the Baltic 

 and the many glacial boulders of the older Paleozoic rocks, which 



o 



are found in the drift in the Aland Islands, Finland, lead to the 

 belief that other areas are beneath the waters of this inland sea. 

 The lower members of the Paleozoic are grouped under the name 

 Siluric which is then subdivided in descending order into Goth- 

 landic, Ordovicic, and Cambric. The Swedish geologists thus 

 follow the lead of ]\Iurchison. We are here chiefly concerned with 

 the contact of the Cambric upon the ancient crystallines. This is 

 of such a character as to prove the old bedrock upon which the first 

 Cambric strata were deposited to have been in general very even. 

 Such relief as can be detected in most of the areas is slight and the 

 old land surface seems to have been worn nearly to a level. 



These observations coincide with the greater part of the observa- 

 tions around the Adirondacks. Professor Gushing has demon- 

 strated the very even sub-Potsdam floor along the north and north- 

 west sides (i)^ and has recently discovered in the southeastern edge 

 much the same relief, although hummocks as high as 100 feet 

 seem recognizable. Doctor Ruedemann has described in some 

 detail the small inliers of gneiss amid the encircling Potsdam at 

 Port Henry. (2) In the quadrangles mapped by Prof. W. J. Miller 

 along the southwestern edge, the same condition is indicated but, as 

 is well known, sedimentary overlap brings several of the Ordovicic 

 members in contact with the Archean. The escarpment of the 

 Medina sandstone in the Little Falls quadrangle led Professor Gush- 

 ing to strongly suspect that it, too, had once extended over the 

 ancient gneisses (3). 



The writer has suggested the original extension of the Ordovicic 

 and Cambric sea up valleys in the Archean along the eastern side 



1 The fij^urcs in i)arciitlu's<.'S refer to the bibliograpliy at the elosc of this 

 paper. 



