LOWER PALAOZOIC ROCKS. 
LYELL, 1871. PHILLIPS, 1855. GEOLOGICAL SURVEY, 1865. 
f Downton Sandstone and Bone Bed. Tilestones. 
Upper Ludlow. Upper Ludlow. 
. Lower Ludlow. e Aymestry Limestone. 
z Z 5 
= | S 4 Lower Ludlow Beds. 
5 
5 Wenlock Limestone and Shale. B 3 | Wenlock Limestone. 
z a 
a Woolhope Limestone and Grit. | a 3 Wenlock Shale with Sandstone. 
> 4 
~ | Tarannon Shales. | =) & Woolhope Limestone and Shale. 
Upper Llandovery, or May Hill. | Denbighshire Grits. 
Lower Llandovery. z Tarannon, or Pale Shales. 
: SO 
e a { Bala and Caradoc Beds. E 2 [ Upper Llandovery Rock, or May Hill Sandstone. 
= Soe 
5 8 + Llandeilo Flags, le 
He f Lower Llandovery Rock, &e. 
Arenig, or Stiper-Stones Group. = | 
E aa | Caradoc or Bala Sandstone, and Limestone. 
= Tremadoc Slat a zi 
a g RETOOL, PENSE Ss Es | Llandeilo Flags and Limestones. 
Ee ’ 3 Bi Bed 
mae Lingula Flags. 5 — 3 3 | Graptolite Shales and Slates. 
ae : ; 7) 
e c Menevian Beds. | , z | Tremadoc Slates. 
Be 4 rise as ; 
8 E | Ease mae | E 3 | Lingula Beds, 
( Harlech Grits and Llanberis Slates. 3 4 Harlech, Llanberis, St David’s, and Longmynd 
= Grits, and Conglomerates with Pale and 
3 Green Slates. 
In 2 communication to the Geologists’ Association (June 1872), on the Classification of the Cambrian and Silurian rocks, 
Dr Hicks nearly followed that adopted by Sir C. Lyell. 
The Lower Cambrian, to include the Longmynd (Harlech grits and Llanberis slates and the rocks at Bray Head) and 
the Menevian groups. 
The Upper Cambrian, to include the Lingula flags (Lower, Middle and Upper, called also the Maentwrog, Ffestiniog and 
Dolgelly) and the Tremadoc groups. 
The Lower Silurian, to comprise the Lower and Upper 
Tremadoc and the true Arenig rocks, the Upper and Lower Llandeilo and the Bal 
The Upper Silurian, to consist of the Lower and. Upper Llandovery, the Wenlock and Ludlow groups. 
Arenig, the former being a connecting link between the 
a or Caradoe groups. 
