of Siluric strata are exposed, ranging in age from questionable Wenlock, through the Ludlow and Lanarkian (Downtonian) and into the volcanic series of the Lower Old Red sandstone. The eurypterids are found in many more localities than in the Pentland Hills, but they are never so abundant nor are so many genera and species represented. There are four important Siluric areas in Lanarkshire, but in only two of these have eurypterids been found, namely in (1) the Lesmahagow inlier, and (2) the anticline of the Hagshaw Hills.
(1) The Lesmahagow Inlier. This is the larger of the two anticlines and extends from a little north of Muirkirk northeast for 6 miles. The Greenock Water in the southwest and the Logan Water in the northeast have exposed a number of excellent sections in the gently dipping beds. The lowest beds exposed consist of a series of blue greywackes with shale partings, the whole comprising 1300 feet as seen along the southern margin of the area along the headwaters of the Ponesk and Nethan. Only a few specifically unidentifiable fossils have been obtained from this series which is provisionally placed with the Wenlock. Immediately to the north of these beds occur grey, blue and olive shales, with occasional nodular greywacke bands yielding a good representation of lowest Ludlow fossils.
The third subdivision recognized by Peach and Horne constitutes the so-called Ceratiocaris beds which are of particular significance because of the surprising abundance in some places of several species of Ceratiocaris, and because of the occurrence of the Ludlow fish, Thelodus scoticus in one layer and finally because of the association of eurypterid remains with both of these. At many different points along the Logan Water the beds are excellently shown. In a small gorge about three-quarters of a mile to the northeast of Logan House the lowest of the Ceratiocaris beds dipping to the northwest are succeeded by some zones of dark, fissile calcareous flaggy shales which weather a rusty brown and which have yielded the following fossils:
- Worm tracks
- Ceratiocaris laxa Woodw. and Jones
- Ceratiocaris longa Woodw. and Jones
- Ceratiocaris papilio Salter
- Ceratiocaris stygius Salter
- Ceratiocaris telson, like murchisoni M'Coy
- Slimonia acuminata Salter
