INTRODUCTION. 
So many years have elapsed since the publication of the second volume 
of the Palaeontology of New-York*, that it becomes proper and necessary 
to preface the present volume with a short review of the results of the 
great progress since made in our knowledge of the successive rock forma¬ 
tions, not only in regard to the higher groups, but also to those treated of 
in the previous volumes of this work. 
Geological surveys, both public and private, have extended over large 
areas of the United States; and the very elaborate Geological Survey of 
Canada, under the direction of Sir William E. Logan, has, more than all 
others during this period, contributed to our knowledge of the older for¬ 
mations. 
Among the important and interesting vestiges of ancient life in the 
Potsdam sandstone, the investigations in the Canadian Geological Survey 
have brought to light the existence of footprints and trails, produced 
probably by crustaceans of several species, and some of them of large size. 
These trails, extending over wide areas of smooth surface, and associated 
with ripplemarks, furnish conclusive proof, if it were still needed, of the 
shallow condition of the ancient sea. It is even certain that these tracks 
are in part or wholly subaerial, since the action of the wind is clearly 
shown upon the ripplemarked surfaces. 
Soon after the publication of the first volume of the Palaeontology of 
New-York, the surveys of Dr. D. D. Owen in the northwest had made 
* This volume bears the date of 1853; but so far as regards the completion of the work, except the 
preface, it was finished in 1851. 
[ Paleontology III.] 1 
