C. E. Dutton on the Contractional Hypothesis. 113 
in the Upper Silurian strata of Gaspé, Canada.* Here, with a 
large number of fucoids, a few specimens have been found, 
which he refers to his genus Psilophyton. In these the scalari- 
form axis and the outer fibrous bark both remain, and serve as 
guides in their classification. 
With these exceptions, no land plants are reported below the 
Devonian. On this point, however, the evidence is all negative, 
and highly auntie. land plants may be at any time found in 
the Lower Silurian rocks. Indeed, the variety and high rank 
of the Devonian flora prepares us to expect such a result. 
Strict accuracy compels us to state, however, that up to the 
aay time positive proof of the existence of land plants in the 
ower Silurian has not been met with in other countries, nor is 
it furnished by the specimens under consideration. 
Art. XI—A Criticism upon the Contractional Hypothesis; by 
Captain C. E. Durron, U.S. A.t 
* Dawson, Precarboniferous Plants of Canada, p. 66. 
+ This paper is one of several communications to the Washington Philosophical 
Society uring the winter of 1872-73, and has not hitherto been published 
xcept by title and brief abstract in the minutes 
Am. Jour. Sci.—Turrp Serres, Vou. VIII, No. 44—Ave., 1874. 
8 
