Distribution of the Rhabdophora. 55 



papers * on the Graptolites of Thuringia, together with the 

 following species : — 



Diplograptus birastrites, Richter. Monogi-aptus testis, Barr. 



Rastrites urceolus, Richter. nuntius, Barr. 



Monograptus priodon, Bronn. turriculatus, Barr. 



gemmatus, Barr. 



all of which, with the exeption of the first two, are probably 

 from strata of later age than the Birkhill Shales. 



Bohemia. — We now enter upon the interesting region of 

 Bohemia, made classic to the student of the Proterozoic rocks 

 by the genius and researches of Barrande. In this area, as 

 already pointed out by Barrande himself, the single division 

 Eel and the hardly separable zone of the colonies are all that 

 represent the British strata interposed between the summit of 

 the Bala and the base of the Upper Ludlow of Murchison. 

 In other words, the Lower and Upper Llandovery, Tarannon, 

 Wenlock, and Lower Ludlow of Siluria find their equiva- 

 lents in a small group of carbonaceous and calcareous strata 

 not greatly exceeding 300 feet in thickness. At the present 

 time all the fossils from this diminutive group are united 

 under a single head, and the collective fauna shows of neces- 

 sity a combination of the characteristics of several distinct 

 British subformations. In Bohemia, precisely as in Britain, 

 the earlier stages of the period of the Third Fauna were 

 marked by repeated elevations and depressions of the sea-bed. 

 An additional local complication was introduced through the 

 prevalence of volcanic action during these early stages, as 

 shown in the abundance of igneous rocks, both interstratified 

 and intrusive, with which the fossiliferous strata are associated. 

 The unconformabilities, overlaps, faults, and folds pointed out 

 by Barrande in these strata are, in all probability, accompa- 

 nied by a host of other physical accidents as yet undetected. 

 When these physical complications shall have been more 

 perfectly unravelled, and the fossils of the beds classified 

 zone by zone, I feel assured that the anomalies which now 

 appear, on a cursory view, to be most naturally accounted 

 for on the hypothesis of successive interchanges of distinct 

 faunas will wholly disappear, and that, as our knowledge of 

 the rocks and fossils of the Proterozoic age increases, the 

 strata of the symmetrical Bohemian basin will be found to 

 admit of minute and satisfactory comparison with those of 

 Britain. 



* Richter, Zeitschrift d. deutsch. geol. Gesellsckaft, vols, for 1850, 1851, 

 1853-1871, &c. 



