Page:The Habitat of the Eurypterida.djvu/167

Rh slight positive one, with the consequent killing off of the fish, a bone-bed would be formed and in a given section would be found overlying a Lingula bed, as does the Temeside Bone-Bed (F d). Were the sea to retreat again, more Lingulae would be left stranded, while fluviatile organisms that were light enough might be floated out across the flood-plains of the rivers. These flood plains had but just been retrieved from the sea and would have been so slightly raised above sea level that only lighter organic remains such as the Lingulae were washed over it, thus fluviatile remains of small specific gravity would be carried out across the flood-plain there to come to rest with the Lingulae, and in this way the olive shales with eurypterid fragments and Lingula cornea would be easily explained. The impossibility of considering either fish or eurypterids as washed in from the sea is indicated by the absence of these forms in the open marine waters to the south. While I have made no attempt to prove the fluviatile habitat of the fishes, yet the bone-beds seem capable of explanation on no other hypothesis. Sometimes the beds are only $$\tfrac{1}{4}$$ inch thick, containing no complete remains but only a great mass of broken bones, spines, and scales. Such an accumulation could be formed only of transported material, the fish skeletons having been entirely scattered. If a bone-bed were accounted for as due to the sudden destruction of fishes in the sea by a current of colder or more saline water, by an earthquake or some other catastrophic calamity, then the fish would die in great numbers, but their remains would be buried in situ. An illustration of this is found in the case of the tile fish off the New England coast, where, in 1882, according to estimates, over one billion fish were destroyed, and the ocean floor was covered in this region to a depth of 6 feet with the bodies of the dead tile fish (Grabau, 87, 195). Entire skeletons would be preserved in the rapid burial, and other marine organisms which suffered the same fate as the fish would also be entombed, so that the resulting deposit would in no way resemble the bone-beds, which are made up of fragments, usually so broken that identification cannot be made, while marine shells are only rarely found.

. The inliers of Siluric rocks are larger in Lanarkshire than in the Pentland Hills, and the succession is shown more completely, for in Lanarkshire the structure is anticlinal, while in the Pentland Hills the beds have been repeatedly faulted and stand nearly vertical, making it impossible to trace an outcrop except along the strike. About 5500 feet