252 TRANSACTIONS OF THE [may 18, 
the older rocks is in the main quite abrupt; in which within 
short distances the Potsdam may be found in patches at heights. 
varying from the lake level (101’ A. T.) to 1500’; in which it is 
not always the Potsdam that is in contact with the older rocks; 
in which basal conglomerates are infrequent, and in which a 
large number of the contacts are unquestionably due to fault- 
ing; in which therefore decisive evidence as to the age of the 
dikes would not be likely to be forthcoming. But the evidence 
on the north is most important. 
All along the northern contact line dikes are of frequent oc- 
currence in the older rocks, and as abundant close to the con- 
tact as away from it. In the wide expanse of Potsdam country 
north of the contact not a single dike has been noted, though % 
careful watch was kept for them, and exposures are frequent 
and often of great areal extent, as in the Flat Rock district, in 
Altona township. In the absence of any specific case of a cut- 
off, this evidence seems very strongly to point to the pre-Pots- 
dam age of the dikes in the older rocks. 
SUMMARY. 
A pre-Cambrian as well as a post-Ordovician period of dike 
formation in the Adirondacks and along Lake Champlain is 
rendered probable because of (1) the much larger number of 
dikes occurring in the pre-Cambrian rocks; (2) the fact that the 
great proportion of the dikes so occurring are of diabase, while 
diabase dikes are not found outside of the pre-Cambrian areas, 
and have a much wider distribution than the other dikes which 
do so occur; (3) the fact that along the line of contact of the 
Potsdam with the older rocks north of the Adirondacks the 
quite plentiful diabase dikes in the older rocks are apparently 
cut off by the Potsdam. 
WESTERN RESERVE UNIVERSITY, 
March 25, 1896. 
THE STRATIGRAPHICAL RELATIONS OF THE 
BROWN’S PARK BEDS OF UTAH. 
By Joun Duer IRvina, A. B. 
(Read May 18, 1896. ) 
Until a comparatively recent date the science of vertebrate 
paleontology was based largely on the study of fossils obtained 
from European and other foreign localities. Between 1871 and 
