GEOLOGICAL DISTRIBUTION. 97 



The only examples of the Galcispongice yet discovered in our area are minute 

 detached spicules in the Carboniferous Rocks of Fifeshire. 



Geological Distribution. 



Cambrian System. — The lowest rocks in which fossil Sponges have been met 

 with are hard, black, slaty beds, belonging to the Menevian series near St. 

 David's, South Wales. The examples of Protospongia occurring in them, have their 

 spicules replaced by iron-pyrites or iron-peroxide. The same genus is present in 

 nearly similar rocks at Krekling and other places in Norway, associated with 

 Paradoxides. 



In hard, slaty rock of the Tremadoc series, near St. David's, the earliest known 

 example of Hyalostelia was discovered by Dr. Hicks, F.R.S. 



Ordovieian System. — In the Llandeilo district of North Wales, at Tre Gil, 

 South of Llandeilo, Pont Ladies, and near Shelve, in Shropshire, the anchoring 

 spicules of Hyalostelia are of not unfrequent occurrence in the hard, dark, 

 calcareous shales of the Llandeilo series. The same genus is present in a dark 

 slaty rock at Dobb's Linn, Moffat, Dumfriesshire, as well as in light grey limestones 

 of Ordovieian age, in the Girvan area of Ayrshire; and from the same rocks 

 Professor H. A. Nicholson has obtained Hindia fibrosa, Roemer. In a slaty rock 

 of Lower-Llandeilo age at Garn, Arenig, Wales, Ischadites makes its first appear- 

 ance. The Caradoc shale of Haverfordwest, South Wales, has yielded a single 

 pyritized example of Astylospongia. 



Silurian System. — Alike in the calcareous shales of the Wenlock and Ludlow 

 series, the genus Ischadites is widely distributed. At Woolhope, in the Dudley 

 and Malvern areas, Usk, near Buildwas, Shropshire, examples have been met 

 with. 



In the Dudley and Malvern areas, spicules of Astraospongia are sparsely present, 

 and near the " Craven Arms," Shropshire, Hyalostelia and Atractosella are found 

 in decayed limestones. 



A well-marked horizon for fossil Sponges occurs in the Pentland Hills, near 

 Edinburgh. The rock is a decayed limestone of Upper-Ludlow age. It is charac- 

 terised by Amphispongia ; examples of Plectoderma and Ischadites also are present 

 in it. At Mocktree, Shropshire, a sandy rock of Aymestry age is characterised by 

 Phormosella ; and the only British examples of Dictyophyton have been met with 

 in arenaceous beds of Upper-Ludlow age, near Kendal, Westmoreland. 



Devonian System. — In the limestones of the typical area of this system, at 

 Newton Bushell, Devonshire, Sphazrospongia occurs ; at the adjacent Newton Abbot 

 detached spicules of Astrceospongia are present in decayed limestones, and at Mud- 



