22 E. W. ELLS ON THE POTSDAM AND CALCIFEEOUS 



stone, the greater portion of which contain a rich Primordial fauna, are now arranged under 

 several distinct heads. 



The term Potsdam sandstone was first applied by Dr. Emmons, in 1837, to a series of 

 arenaceous deposits which were well developed in the vicinity of the village of Potsdam, in 

 the northern part of the state of New York. In his report on this area Dr. Emmons 

 describes the occurrence of certain sandy and calcareous layers Avhich he styled the Potsdam 

 sandstone and Caleiferous sandrock, the former of which reposed directly upon the primitive 

 rocks, now known as Laurentian.' 



This term Potsdam sandstone was afterwards adopted by Logan in his investigation of 

 the geological formations in Canada and applied to a similar series of sediments which, in the 

 Ottawa basin and at certain places along the St. Lawrence, occupied a similar position upon 

 the Laurentian gneiss and limestones to that found by Emmons in New York. These were 

 regarded by Logan in the earliest stages of geological investigation as constituting the basal 

 portion of the Pala?ozoic series. The formation can be traced directly into Canada from the 

 place where originally studied in New York state, and there can be no doubt as to the 

 similarity of the strata and the equivalency of their horizons. 



The basal beds of the Potsdam sandstone both in New York and Canada are made up of 

 the debris of the underlying Laurentian rocks. They thus present for several feet a regular 

 conglomerate structure, but this speedily passes into a sandstone, largely quartzose, of a 

 grayish or yellowish-gray colour. This gradually changes through sandy beds into others con- 

 taining a proportion of calcareous matter till it passes without break into the regular 

 Caleiferous formation. 



In the study of the geology of New York and Vermont states, it was held by the earliest 

 geologists, among whom may be mentioned Dr. Amos Eaton (1818) and Dr. E. Emmons 

 (1842), that the Potsdam sandstone was a formation distinct from and above a series of 

 other quartzose and slaty rocks, known at the time as the granular quartz and the Georgia 

 slate groups, which were regarded as of Cambrian age. Subsequent examination of the rocks 

 of this district by diiferent investigators resulted in the expression of a variety of opinions. 

 By some of these it was held that all these rocks, together with the Potsdam sandstone, were 

 on the same horizon, while others placed them at the summit of the Lower Silurian system. 

 The various opinions on this subject have been already stated by Marcou, Hunt, "Walcott 

 and others, so that it is not considered necessary to cover again the ground so ably reviewed. 

 The " Taconic controversy " has long been matter for history, and it is moreover, to a large 

 extent, beyond the scope of the present paper. 



The description of the typical Potsdam sandstone cannot perhaps be better stated than 

 in the words of Dr. Emmons himself He says, " this rock is a true sandstone of red, 

 yellowish-red, grayish or grayish-white colours. It is made up of grains of sand, and held 

 together without a cement. Intermixed with the siliceous grains are finer particles of 

 yellowish feldspar, which do not essentially change the character of the sandstone, but they 

 show the probable source from which the materials forming it were originally derived, viz , 

 some of the varieties of granite. Unlike most of the sandstones, however, it is destitute of 

 scales of mica. The colouring matter of the rock is evidently oxide of iron, but unequally 

 diffused through it, giving it intensity or deepness of colour in proportion to its quantity. In 



' Geol. Rep. N.Y., 1837, pp. 214, 217, vol. I. 



