212 AMADEUS W. GRABAU 
rock which elsewhere carries them, indicates some peculiarity of the 
sea-shore at that point, capable of barring the life of the sea, is a 
laborious explanation to fit a preconceived notion of the origin of the 
formation in question. Nor must we forget that the North American 
continent was above the sea during long periods of pre-Cambric and 
Cambric time, and that on those vast land areas subaérial deposition 
as well as erosion must have been in progress. It is therefore to be 
expected that in many, if not in most, regions the Paleozoic series 
begins with a formation of continental origin, the upper portion of 
which was reworked by the transgressing sea, and became incor- 
porated as a basal member of the marine series succeeding. In 
this manner the contact between the continental and marine series 
often became an apparently conformable and perfectly gradational 
one, the hiatus between them being masked. It will of course be 
impossible in such a case to determine whether a basal bed of con- 
tinental origin is of pre-Cambric, of Cambric, or of post-Cambric 
age; all that. can be determined is the period at which its upper 
portion was reworked by the transgressing sea. If the basal bed is 
of slight thickness it is in such a case best referred to the age of the 
immediately succeeding marine formation. 
The question naturally arises, should the lower portion of the 
Beekmantown be referred to the Cambric with which it forms a 
continuous transgressive series, or should it be retained in the Ordo- 
vicic with the remainder of the Beekmantown? While in New York 
the fauna is, so far as known, an Ordovicic one, in other localities 
beds considered of the same age carry a mixed Cambric and Ordo- 
vicic fauna. In this respect these beds and the typical Saratogan, 
as well as the St. Croix series of Minnesota and Wisconsin, probably 
correspond to the Tremadocien of Europe, which is classed as Upper 
Cambric by British geologists, but by German and other continental 
geologists as basal Ordovicic (Unter Silur). Matthew correlates these 
beds with the Asaphellus homjrayi beds of the St. John section, 
and so places them above the Dictyonema flabellijorme beds, which 
at present are also included in the base of the Ordovicic by some 
continental geologists. That such transitional formations are to be 
expected in any complete depositional series is, of course, obvious, 
and their precise reference is a matter of secondary importance. 
