292 W. D. MATTfiEW PHYLOGEXY AND CORRELATION 



not been faunal, but more or less sporadic, and all in one direction ; 

 and local adaptive radiation has caused progressive evolution, the result- 

 ing parallelism and convergence adding new difficulties to the correla- 

 tion problem. It is doubtful whether such correlations can ever be cor- 

 rectly and accurately made except on diastrophic criteria, and for this 

 method our data are not yet sufficient. 



