De Geer.] 
470 
[May iS, 
submergence formed a narrow strait across the Chignecto Isthmus 
the figures for the localities at St. John and in Nova Scotia are 
perhaps some 5 feet too high. If, as is probable, the levelings 
based upon railway altitudes refer to mean tide, they also must 
be lowered about 5 feet. 
The levelings were all made with Swedish handlevels con- 
structed by Wrede and Elfving, which contain a mirror held 
vertically by an adjustable weight and sheltered from the 
wind by a little wooden case. By aid of a scale angles can also 
be measured and I have often made good use of them as a check 
and also for plane table work. 
The barometrical measurements were made with two aneroids 
from Naudet in Paris, and each is based upon a series of 10 
to 25 observations by means of which the changes in pressure 
during the day are graphically constructed, and from the differ- 
ences thus obtained the height is reckoned with due correc- 
tions for temperature. Though I have often in this way got 
remarkably good results, it is very desirable that these measure- 
ments should be checked by the spirit level, as figures should not 
be considered conclusive which have not an accuracy within three 
feet or about one meter. 
Conclusions. 
All the observations on the height of the marine limit have been 
put down on the accompanying general map, and with aid of 
interpolation isobases have been drawn through equally uplifted 
points with an interval of 200 feet (60 m.). 
Concerning the extension of the isobases into the interior of the 
continent, where the marine limit could not be directly de- 
termined, I have tried to use interpolation in the following 
manner. As has been stated, it is probable that the geoid-sur- 
face, which in the submerged regions is marked by the marine limit, 
is situated in the tract northeast of Lake Ontario at a height some- 
whatless than 75% of the older high-water level recorded by the 
Iroquois beach. From the figures given by Professor Spencer 1 
we find that this beach is situated at about 36% of the Ridgeway 
beach at the three localities where both occur near each other. 
1 High level shores in the region of the Great Lakes and their deformation. Amer, 
jonri"-. ofsci,, March, 1891, 
