Page:The Habitat of the Eurypterida.djvu/126

 can be followed through in the same way for the Kokomo, the most marked difference between the two formations being the local character and diverse source of the latter. The Kokomo waterlime lacks the lateral and vertical persistence characteristic of the Bertie and in this respect is similar to the waterlimes of Oesel which in many outcrops appear as thin bands intercalated between limestone beds (see section, fig. 7 above, and description). Indeed, the section revealed at Kokomo is the counterpart of what theoretically we should expect to find in the southward continuation of the Bertie in Pennsylvania where the waterlimes merged into the marine deposits.

The second difference between the Kokomo and Bertie waterlime is that of origin, for while the latter was derived from the north the former must have come from the west since the sea covered the Michigan area during Monroe time and precluded the derivation of sediments from the Canadian region. It is difficult to arrive at an explanation of the lithogenesis of such a formation when so few outcrops are visible, but yet we can determine enough to show that the Kokomo sediment was river-borne and came from a continent to the west (see map, fig. 8). A study of the faunas convincingly shows the distinctness of the source of the material and organisms found at Kokomo (see below, pp. 253-256).

. The clearest conception of the lithogenesis of the eurypterid-bearing Wenlock beds of southern Scotland is to be obtained from a survey of the palaeographic conditions existing in Great Britain from the end of Ordovicic time on through the Siluric. The outcrops in Wales, in the hilly areas of Cumberland and in innumerable outliers in Westmoreland and elsewhere, as well as those of the southern uplands of Scotland, indicate that throughout the Ordovicic the sea covered Wales, the greater part of western and central England and southern Scotland as far north as the great northeast-southwest fault line delimiting the northern edge of the tableland. The central and northern portions of Scotland formed a part of the old land which, rising to the east in the Scandinavian shield, extended westward through North Britain and Ireland on into the northern Atlantic, and which throughout the Palaeozoic furnished the sediments which were deposited either in the sea to the south of that ancient shoreline, or on the land to the north of