398 Review of the Progress of 
The Potsdam sandstone of the St. Lawrence valley, has for 
the most part the character of a littoral formation, being made 
up in great part of pure quartzose sand, and offering upon suc- 
cessive beds, ripple and wind marks, and the tracks of animals. 
Occasionally it includes beds of conglomerate, or as at Hemming- 
ford, encloses large rounded fragments of green and black shale; 
it also exhibits calcareous beds apparently marking the passage 
to the succeeding formation, which although called a Calciferous 
sandrock, is for the most part here, as in the west, a magnesian 
limestone, often geodiferous, and including calcite, pearl spar, 
gypsum, barytes and quartz. Sir William Logan had already 
shown that the fauna of the Potsdam and Calciferous in Canada 
are apparently identical, (Can. Nat., June, 1860; This Journal, 
[2], xxxi, 18), and Mr. Hall has arrived at the same conclusion 
with regard to the rhore extended fauna of these formations in the 
valley of the Mississippi, so that these two may be regarded as 
forming but one group. While in the west Dikellocephalus oc- 
curs both in the lower sandstones and the magnesian limestones, 
Conocephalus minutus, found in the Potsdam on Lake Champlain, 
and identified by Mr. Billings, has lately been detected _by him 
in specimens from the sandstones of Wisconsin with Dikelloce- 
phalus, which aes has there been found to pass upwards into 
the magnesian limestones. On the other hand, the sandstones of 
Bastard in Canada, having the characters of the Potsdam, con- 
tain Lingula acuminata and Ophileta compacta, species regarded 
as characteristic of the Calciferous, together with two undeseril 
species of Orthoceras, and in another locality a Pleurotomaria re- 
sembling P. Laurentina. The researches of Mr. Billings have 
seozoic system, attain in Virginia a thickness of 1200 feet, and 
Primal slates, consisting of 700 feet of greenish and brownish 
talco-argillaceous shales with fucoids, ‘To. 
et a 
