136 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



the thinner ones, are fine-grained, and we should 

 expect Ostracoda to turn up in them. The great 

 bulk of the species are got in the shale both above 

 and below the Wenlock Limestone. In the shales 

 in connection with the Aymestry Limestone, Ostra- 

 coda are either very rare or altogether absent. 



The Silurian shales are generally of a yellowish 

 colour, but possibly this colour is only confined to 

 the strata near the outcrop of the beds, and is very 

 likely to be the result of hydration. The shales are 

 sometimes of a bluish or bluish-green, and in one 

 instance of a red colour. The mineral matter which 

 makes up the bulk of the shales is exceedingly fine- 

 grained, and contains occasional particles of angular 

 and well-rounded quartz ; and as these particles 

 gradually increase in quantity in a shale the 

 microzoa gradually become fewer, both in individuals 

 and species, although there are some rather fine- 

 grained shales in connection with the Aymestry 

 Limestone in which microzoa are very scarce. 

 Minute scales of mica are more or less frequent in 

 all the shales, and they generally increase in quantity 

 along with the quartz-grains. The mica is generally 

 white, sometimes brownish, and rarely brass-coloured. 

 In one shale the microzoa were dusted over with 

 very minute mica-scales. In many of the shales 

 small brownish magnetic particles turned up. May 

 these be meteoric dust? In one gathering near the 

 Malvern Hills were small fragments of hornblend, 

 felspar, and obsidian or pitchstone. In nearly all 

 the shales small fragments of black scoriaceous lava 

 were got. 



The minerals above referred to have evidently 

 been deposited along with the shales, but the 

 following have been formed chemically after the 

 shales were deposited : prismatic and crystallised 

 transparent and opaque calcite ; small more or less 

 rounded white crystalline aggregates of calcite ; 

 hematite (rarely) ; minute cubes, spangles, and amor- 

 phous iron pyrites ; and galena (in one sample). In 



