Page:The Habitat of the Eurypterida.djvu/137

Rh could lead to any other conclusion but that the eurypterids dwelt in the Wenlock sea? It is just because such a conclusion in reality is entirely unjustifiable that I was led to state at the beginning of this paragraph that the eurypterid occurrence in the Wenlock is the most significant one in the British Isles when its interpretational value is taken into account.

. The Pentland Hills are formed from a series of the folded pre-Devonic beds and are completely surrounded by the various sub-divisions of the Old Red sandstone and by the igneous rocks. The Siluric rocks are exposed in four small isolated patches in these hills, and yet in spite of the small size of the outcrops and their isolation they have yielded more species of eurypterids than any other single formation in the world, with the exception of the Bertie waterlime, though there is this marked difference between the two faunas: whereas the Bertie fauna contains the most perfectly preserved individuals that have yet been recorded from any locality, with the exception of those from Oesel, the Pentland Hills fauna, on the other hand, is made up, for the most part, of fragmentary individuals.

The most important of these four inliers is that extending from the head of Lyne water to the head of North Esk River, a distance of about three miles. Although this inlier is the largest of the four it covers an area of only about two to three square miles. A number of excellent sections have been opened up by the North Esk and its various tributaries. The river itself cuts across the outcrop nearly at right angles, and since the beds here as in the other inliers are strongly folded, standing on end with the strike northeast-southwest, a considerable range in age is shown in the section, the lower beds appearing to the east, in the North Esk section where the Wenlock, Ludlow and a portion of the Lanarkian (Downtonian) are exposed, while to the west the Lyne water cuts through the passage beds or Downtonian. Of the numerous sections thus exposed the one which has now become most famous on account of the large eurypterid fauna discovered there by Hardie and Malcolm Laurie is that on the Gutterford Burn, a small tributary of the North Esk. (See map, fig. 12.) On the east bank of the burn, about a half a mile up from the North Esk Reservoir the strata consist of "flaggy micaceous greywackes" dipping at about 80 degrees to the southeast. Peach and Horne give a list of the fossils which they state come "from this band" (215, 593), but one may question the accuracy of this statement when