GEOLOGY AND MINERALOGY. 149 



PRIMORDIAL SAND8T0NK OP THE ROCKY MOUNTAINS. 



Dr. F. V. Hayden has sent us a very interesting paper, reprinted from a late 

 number of the American Journal of Science and Art, on the " Primordial Sand- 

 stoile of the Rocky Mountains in the North-Western Territories of the United 

 States." The wide occurrence, in that region, of sandstones and conglomerates 

 resting -immediately, but unconformably, on rocks of Azoic age, and containing 

 fossil types of the Primordial or Potsdam sandstone zone, as recognized in New 

 York, appears to be fully established. We quote from Dr. Hayden's concluding 

 remarks the following analytical summary of the various points discussed in his 

 communication : — 



" 1. We have the most undoubted evidence of the existence of that division 

 of the Primordial Zone which is the equivalent of the Potsdam sandstone of the 

 New York series, in two important ranges of mountains, outliers of the great 

 Rocky Mountain chain. All the fossils are well known Primordial types, and 

 at least two species are identical with forms occurring at the typical localities 

 of this period in the Eastern States. The others are forms closely allied to 

 species found in the equivalent rocks both iu this country aud in Europe. 



" 2. This division of the Primordial Zone, as a rule, appears as an underlying 

 formation when the conditions are such as to expose it to view, from the Atlantic 

 coast to the crest of the Rocky Mountains, and probably farther. Localities 

 doubtless do occur where rocks of more recent age than the Potsdam sandstone 

 rest directly upon the Azoic or granitic rocks below, but these facts do not mil- 

 itate against the general rule. Having proved its existence in two important 

 ranges of mountains from its organic remains, by means of lithological resem- 

 blance and stratigraphical position, we have, with considerable confidence, 

 traced it by personal observations throughout the mountainous district comprised 

 within lat. 40° and 49°, and Ion. 103° and 112°. From these facts, and the 

 observations of reliable explorers in different parts of the West, we think we 

 are warranted in the belief that this rock is exposed all along the margins of the 

 Rocky Mountain range when not ei-oded away or concealed by overlying forma- 

 tions. How far westward of the dividing crest of the Rocky Mountains it 

 extended we have no data for determining, nor can we hope to have where 

 eruptive rocks seem to predominate. As yet we have not known the Potsdam 

 sandstone to be exposed except along mountains with a true granite nucleus. 



" 3. Wherever this rock occurs, we are struck not only with the singularity of 

 the organic remains, but also with the remarkable uniformity in the nature of 

 the sediments and the general lithological appearance, compared with its equi- 

 valents in more eastern localities. We do not believe this to be due to currents of 

 water bearing the materials from far eastern lands, but that the sediments were 

 obtained from the vicinity, and that the uniformity in their character arises from 

 the nature of underlying rocks from which they were derived. 



" The Potsdam sandstone is everywhere composed of calcareous and silicioua 

 matter, granular quartz, ferruginous material in great quantities, also pebbles of 

 various kinds, worn and unworn, with now and then seams and layers of argil- 

 laceous material. We find in the Azoic rocks below an abundance of limestone, 



