GEOLOGICAL SECTION OF NEW JERSEY 355 
fauna below and the Dikelocephalus fauna above. In one locality 
a fauna of Ordovician (Beekmantown) age has been found in beds 
near the top of the Kittatinny limestone. ‘This formation, therefore, 
where complete, represents a period extending from the middle or 
upper part of the Lower Cambrian to the lower part of the Ordovician, 
inclusive. 
ORDOVICIAN SYSTEM 
In northern New Jersey, as elsewhere in the great Appalachian 
valley, there is no sharp line of demarkation between the rocks of the 
Cambrian and those of the Ordovician system. The base of the 
Ordovician lies somewhere below the top of the Kittatinny limestone, 
as stated above, but the exact position of this division line cannot 
readily be determined. 
Jacksonburg limestone-—Above the Kittatinny limestone, and 
separated from it by a break in sedimentation indicated by a calcareous 
basal conglomerate, is a dark-blue or black fossiliferous limestone, 
correlated with the Lowville, Black River, and lower Trenton lime- 
stone of the New York section and hitherto classed as “Trenton,”’ 
some layers of which contain as much as 95 per cent. or more of 
calcium carbonate. Calcareous shales occur interbedded with these 
limestones and above them to the top of the formation. ‘The sequence 
of conglomerate, limestone, and shale is a variable one, but, so far 
as observed, the transition to the overlying formation is always 
through a series of calcareous shales which become less and less limy. 
The thickness of the Jacksonburg formation varies from 135 to 
300 feet or more. It contains an abundant fauna, ninety-eight forms 
having been described by Weller. At the type locality the lower 
strata for a thickness of fifty-eight feet carry a Lowville-Black River 
fauna, and the higher beds have a lower Trenton fauna. 
Martinsburg shale-—The Jacksonburg limestone passes upward 
through the calcareous shales mentioned above into a great thickness 
of shale, slate, and sandstone, which has heretofore been known as 
the ‘‘ Hudson River slate,’’ but which is now correlated with the Mar- 
tinsburg shale of West Virginia and takes that name. 
The formation ranges from the finest-grained shale and slate to 
fine sandstone. The former beds on the whole are black and more 
abundant in the lower part, whereas the sandstone beds are dark 
