§ 1. Introduction . T he several memoirs by Professor Sedgwick on the older Palæozoic rocks of the north of England, published in the ‘Transactions’ and ‘Quarterly Journal of the Geological Society,’ have indicated the nature and the arrangement of the older Palæozoic rocks as they occur in the Lake-district. Among these rocks, and forming the base of the sedimentary series in the north of England, is a mass of strata designated the Skiddaw Slates by Professor Sedgwick, from the circumstance that these slates comprise the Skiddaw range of mountains. They have hitherto been regarded as all but unfossiliferous, the described organic remains consisting only of two species of Graptolites and four forms which have been attributed by Professor M'Coy to Fucoids. The Skiddaw slates occupy a large area in the northern portion of the Lake-district. They also occur in the south-western extremity of Cumberland, where they form the mountain of Black Comb; and they are seen in Westmoreland on the eastern margin of the Lake-district, exhibiting themselves in three small patches. The object of this memoir is to point out in detail the circumstances under which they occur in their several areas, and to show that they are more fossiliferous than they have hitherto been regarded, and also to point out their equivalents elsewhere. § 2. The Skiddaw Slates of the West Side of Derwentwater, Bassenthwaite, and Binsey Crag . The Skiddaw slates on the west of Derwentwater and Bassenthwaite Lakes, and Binsey Crag, form a portion of the area where they