Base of. the Taconic or Loirer Vauihrijdi. — M'/'iiclie//. 157 
ord of progressive evolution, synchronous on both sides of the 
Atlantic. 
With tliis brief reference to the condition of geological opin- 
ion as to the base of the Cambrian in Britain, we wish now to 
call attention to the condition of geological opinion as to the 
l)ase of the Taconic system in America. We shall iind a great 
similarity of fact and of progress in research. 
That there was a long period of pre-'J'aconic time during 
which the older strata, whatever their origin and composition, 
were flexed and rendered holo-crystalline, is generally admitted. 
There is a marked change from this crystalline condition in 
which it is sometimes difticult to discover any remaining 
proof of sedimentation, to the clastic Taconic strata. This 
transition is marked also by a profound non-conformity, the 
wide extent of which has been recognized by several recent 
writers. It is not intended here to say that no clastic struc- 
tures are found below this break, nor that no crystalline rocks 
are found above. In fact clastic structures are very ap- 
parent in those rocks older than this break, but in that case a 
metamorphic re-cr^-stalli/.ation usually accompanies them; 
and everywhere without exception in America, so far as 
known, such elastic strata are so higldy tilted that verticality 
is their normal position. It is a fact also that some of the 
Taconic strata have been affected by a similar metamorphism. 
It is found, however, that when thus disturbed the Taconic 
strata attain verticality only in exceptional cases and in small 
areas, while the massive crystallines wiiicli are found associa- 
ted with the Taconic elastics are, as a class, of wholly dilf'er- 
ent characters from those which preceded the great non-con- 
formit}'. The pi'esence of these characteristic crystalline 
masses in immediate proximity with the occasional sharp 
folding and iiK^tamorphism of the Taconic, serves, with other 
means which need not here he mentioned, for the distinguish- 
ing of the later strata from the older when they are both pres- 
ent in a region. While tiiese broad distinctions can bedrawn 
it must l)e admitted still, tiuit tiie}' have not ahva3's been ob- 
served, and that there is, consecjuently, not a unanimity of 
opinion as to the age of the rocks at this horizon in various 
parts of the United States and Canada. That which we wish 
to jjarticularly emphasize as an important fact in Aiiieric;in 
