GEOLOGY 



RECENT PROGRESS OF GEOLOGY. 



The researches which M. Barrande has made upon the Silurian system 

 of Bohemia have recently been published. They imbody the fruits of 

 more than twenty years' labors ; and his labors and results now place 

 him in the foremost rank of living geologists and paleontologists. The 

 number of fossils he has collected and described from the Silurian system 

 is about 1200. M. Barrande distinguishes eight stages of strata, to wh'ich 

 he assigns a Silurian age ; four of them, he regards as Lower Silurian, and 

 four as Upper Silurian. Of his Lower Silurian stages the two lowermost 

 are azoic, the distinctions between them being founded on mineral charac- 

 ters, the first being composed of crystalline rocks, and the second of clay- 

 slates and conglomerates, similar to the fossiliferous Silurian above them, 

 but wholly destitute of organic remains. These azoic stages pass into 

 each other, and the upper section passes gradually into the fossiliferous 

 beds above. The third stage of his Lower Silurian, and the first of his 

 fossiliferous horizons, attains a thickness of 1200 feet, and contains no 

 beds of limestone. The fauna of this section is very peculiar ; it is com- 

 posed almost wholly of trilobites and a few other fossils. These consti- 

 tute a fauna upon which he lays great stress, and designates as primordial. 

 All the species are peculiar to itself, and the genera are low and rudi- 

 mentary, not typical and highly- developed forms. 



In Wales, and some other Silurian districts, this primordial fauna has 

 also been clearly made out. The rocks which contain it are those des- 

 ignated by Prof. Sedgwick as the Lingula beds. 



The fourth and uppermost division of M. Barrande's Lower Silurians is 

 composed of quartzose strata, with schistose alternations. Cephalopoda, 

 Gasteropoda, Acephala, Brachiopoda, a few corals, starfish, crinoids, make 

 up, with trilobites, the fauna of this group in Bohemia. Trilobites pre- 

 vail above all other forms, and here attain their maximum development. 



Of the four stages of the Upper Silurians in Bohemia, the three lower 

 divisions are typically calcareous, and the culminant section schistose. 

 The lowermost stage is astonishingly rich in fossils, containing between 

 500 and 600 species. The second stage presents a decreasing fauna, and 



