1/0 PALEOZOIC TIME LOWER SILURIAN. 



Lingula flags, like those of the New York and Western Potsdam. 

 In northwest Scotland, beds referred to the Cambrian, consisting of 

 red and purple sandstones and conglomerates, overlie unconform- 

 ably the crystalline Azoic, — " the fundamental gneiss" (Murchison). 



It should be here stated that Murchison places these Cambrian 

 beds on the same horizon with the Huronian of Canada. The cor- 

 rectness of this inference is not yet fully established. A large 

 portion of the crystalline rocks and schists of the Highlands pf 

 Scotland are metamorphic rocks of the Silurian age. 



In Lapland, Norway, and Sweden, there is a Primordial sandstone 

 overlaid by schists, the lowest beds passing at times into a conglo- 

 merate. They are the regions A, B of the geologist Angelin. 

 In Bohemia, the lowest Primordial beds are schists 1200 feet thick, 

 called by Barrande Protozoic schists, or the Primordial Zone, and 

 numbered C in his series, — his A, B consisting of schists and con- 

 glomerates conformable to C. Until recently B was thought to 

 contain no trace of life, and therefore to be below the Primordial ; 

 but within a short time worm-burrows have been reported by Dr. 

 Fritsch to occur in some of these inferior beds. The formation C 

 has been regarded as the equivalent of the Potsdam ; but it may 

 be necessary to add a part or all of B. Barrande's next division, 

 lettered D, consisting of schists, sandstones, and conglomerates, 

 corresponds to the rest of the Lower Silurian ; but the lower por- 

 tion of it may represent the Calciferous epoch. 



II. Life. 



1. American. 

 As the life of the Potsdam period is the beginning of the system 

 of life deciphered in American geological history, great interest 

 attaches to it. 



1. Plants. 



Algce, or Sea-weeds, are the only plants distinguished ; the species 

 are related to the Fucoids, or leathery sea-weeds, of existing coasts 

 (p. 167). 



In general, the remains are stony, vermiform, branching fossils, wholly desti- 

 tute of the original vegetable material. But in some places thin seams of 

 mineral coal have been found beneath or near fucoidal layers ; and in Herkimer 

 co., N.Y., the quartz crystals sometimes contain fragments of anthracite. The 

 lowest of these distinct fucoidal layers in New York occurs in the inferior 

 part of the Calciferous beds : it abounds in slender branched but irregular stems, 

 called Palseophycus irregularis H. (the name of the genus being from the Greek 

 for ancient Sea-weed or Fucus). In another and higher layer, the stems are as 



