Notices of Memoirs — Three Papers on Graptolites. 179 



general matrix of the rock surrounds the balls or nodules of orthoclase 

 "without any intermediary concentric oligoclase layer. 



Microscopically it differs also from the other variety in being 

 destitute of microcline. It occasionally shows micro-pegmatitic 

 structure ; and its quartz is peculiar, being very idiomorphically 

 developed and containing long needles (microliths) of a dark-coloured 

 mineral which the American geologist Hawes declares to be rutile. 



In its stratigraphical relationships the western rapakivi is very 

 interesting, a great deal of evidence having been collected tending 

 to show that it has both exercised an enormous pressure on the rocks 

 through which it has been forced, and has itself in places been 

 modified by this pressure, which may perhaps justify the assumption 

 that it was in a very pasty condition when irrupted. The southern 

 rapakivi on the contrary does not appear to have modified the sur- 

 rounding rocks at all. 



Great masses of granite, syenite, and elseolite-syenite occur 

 throughout the country ; but as they do not on the whole differ from 

 similar rocks in other districts, I have not devoted any space to 

 a descrijDtion of them. 



The various questions relating to the origin, characteristics and 

 occurrence of pegmatites, I propose to reserve for future consideration. 



Three Papers on Graptolites. 



1. Ueber das Alter des sogen. Graptoltthen-Gesteins mit 



BESONDERER BeRUCHSICHTIGUNG DER IN DEMSELBEN ENTHALTENEN 



Graptolithen. Von Herrn Otto Jaekel, in Berlin. Zeitschr. 

 d. deutschen geolog. Gesellschaft, Jahrg. 1889, pp. 653-716, 

 Taf. xxviii. xxix. 



2. GoTLANDS Graptoliter. Af Gerhard Holm. Bihang till K. 

 Svenska Vet.-Akad. Handlingar, Bd. 16, Afd. iv. No. 7 (1890), 

 pp. 1-34, Taf. 1, 2. 



3. Undersokningar ofver Siljansomradets Graptoliter. Af Sv. 



Leonh. Tornquist. Lunds Univ. Arsskrift. Tom. xxvi. pp. 1-33, 

 Taf. i. ii. 



1. On the Age of the so-called Graptolite Stone, with Special 

 Reference to the Graptolites contained therein. Bj'^ Otto 

 Jaekel. 



2. The Graptolites of the Island of Gotland. By Gerhard 



Holm. 



3. An Examinaton of the Graptolites of the District of Siljan, 



Dalarne, Sweden. By Sv. Leonh. Tornquist. 



SCATTERED through the Drift of Northern Germany there are 

 numerous boulders of calcareous rock containing, with various 

 other fossils, several species of Graptolites, and for this reason they 

 were styled " Graptolithen-gestein " by Ferd. Roemer. The parent- 

 rock of these boulders, situated somewhere in the Silurian basin of 



