﻿REPORT OF THE DIRECTOR I9IO 97 



as do the Cambro-Siluric strata. The largest area is in middle 

 Sweden along the boundary with Norway. The Jotnian sandstones 

 exhibit perfectly preserved suncracks and ripplemarks and may dis- 

 play but little in the way of metamorphism. 



The sandstones and diabases along the beautiful coast of eastern 

 central Sweden in the district of Nordingra were shown to the visit- 

 ing geologists. The sedimentary characters were as well preserved 

 as in our Siluric Medina sandstone, as for instance at Lockport, 

 and the grade of metamorphism was scarcely greater. This recent 

 aspect led earlier observers to correlate the sandstones with Paleo- 

 zoic formations, notably the Old Red Sandstone, but the Precam- 

 bric age is now very well established (4, p. 10-11). 



The floor of older rocks beneath the Jotnian is very even so far 

 as visible and reminds one of the floor beneath the Cambric. The 

 foundation rocks are, however, devoid of products of weathering 

 and seem to have been swept clean by the oncoming waters. The 

 Jotnian sandstones, sometimes many hundred meters thick, far sur- 

 pass the Swedish Cambric, and since the quartz grains in them 

 were probably freed by the weathering of older rocks the sub- 

 Jotnian time interval is believed to be far greater than the sub- 

 Cambric. 



One extraordinary feature of the eruptives is the curious 

 " Pebble diabases " near Brevik, in central southern Sweden. Dikes 

 of diabase are so fully charged with rounded boulders, that the 

 observer can only interpret them as follows : it appears that a loosely 

 compacted conglomerate, or even a boulder bed, has been pene- 

 trated and suffused with a basaltic magma as with so much water ; 

 on chilling, the result was a rock almost like a conglomerate, with a 

 basalt bond or cement. We have few parallels for these rocks in 

 America, but one is reminded of a dike at Nash's Point, Vermont, 

 where a trachytic magma is surcharged with boulders derived from 

 lower lying formations, although it now cuts Ordovicic slates (8). 



In the table of formations given above, under Jotnian is men- 

 tioned a group of sub-Jotnian igneous rocks. A brief outline 

 of these will serve also to explain the methods of correlation 

 developed by the Swedish and Finnish geologists when dealing 

 with igneous and metamorphic rocks in disconnected areas. The 

 Jatulian period closed with strong folding, as will be later brought 

 out. Subsequent to the folding there appeared in Finland ex- 

 tensive intrusive masses of a peculiar granite, of coarse porphy- 

 ritic texture. The porphyritic crystals may be one to two inches 



