Revieivs — P. Pocta^s Chalk Sjjonges of Bohemia. 281 



in the second chapter of the present paper. The appearance of 

 intrusion into the adjacent sedimentary beds in such cases is delusive, 

 and is better explained on the supposition of a knob of hard rock 

 which had resisted atmospheric erosion better than the encasing 

 schists, so as to form a boss against which beds of a later age were 

 deposited. Subsequently movements took place resulting in sucli 

 complicated geognostic relations between these hard old knobs and 

 the softer Mesozoic or Tertiary sediments, as to simulate the appear- 

 ance of intrusion. 



Lastly, it should be mentioned that Dr. Stapff, " the learned and 

 acute geologist of the St. Gothard tunnel," speaks of movements 

 arrested by the hard and tough mass of the serpentine, met with 

 during the excavation, as having produced in the neighbouring rocks 

 " perturbations much more intense than would have resulted from 

 similar movements acting upon a more tender rock." Dr. Stapff 

 regards the serpentine of St. Gothard tunnel as "originally a deposit 

 of hydrated silicate of magnesia, formed by springs, and enclosed be- 

 tween the sediments which gave rise to the mica-schists." W.H.H. 



II. — Beiteage zur Kenntniss der Spongien dek bohmischen 

 Kreidefoemation. Von Philipp Pocta. I. Abtheilung : 

 HexactinellidEe. Mit 5 litho. Tafeln und 19 fig. im Texte, 1883. 

 II. Abtheilung : Lithistidse. Mit 2 lith. Tafeln und 26 fig. im 

 Texte, 1884. (Abhandlungen der Koniglichen bcihm. Gesell- 

 schaft der VVissenschaft, VI. Folge, 12 Band.) 



Ueber isoliete Kieselspongiennadeln aus der bohm. Keeidefor- 

 MATioN. Von Philipp Poota. Mit 2 Tafeln. (Aus den Sitz- 

 ungsberichten der k. bohm. Gesellschaft der Wissenschaften. 

 Prag, 1881.) 



Contributions to the Knowledge of the Sponges of the 

 Bohemian Chalk-Formaiion. By Philipp Pocta. Part I. 

 Hexactinellidge. With 3 lithograph plates, and 19 figs, in the 

 text 1883. Part II. Lithistidse. With 2 lithograph plates, and 

 26 figs, in the text. 4to. (Memoirs of the Eoyal Bohemian 

 Science Association. Prague, 1884.) 



On Detached Siliceous Sponge Spicules froji the Bohemian 

 Chalk- Formation. By Philipp Pocta. With 2 plates. 8vo. 

 (From the Sessional Reports of the Eoyal Bohemian Science 

 Association. Prague, 1884.) 



THE stimulus which has been given to the study of fossil sponges 

 by the publication of Professor Zittel's elaborate work on the 

 structure and affinities of these organisms, is shown by the various 

 memoirs now appearing in this and other countries, in which these 

 forms are arranged according to the new system of classification 

 proposed by Zittel. Herr Pocta has undertaken the laudable task of 

 investigating the minute characters of the sponges met with in the 

 Ci'etaceous rocks of Bohemia, and the works quoted above contain 

 the results of his studies of the Hexactinellida3, Lithistidce, as also 

 of the detached spicules of the MonactinellidaB and Tetractinellida3. 

 The form and other macroscopic characters of many of these sponges 



