rare condition of the fossils. After tens of millions of years the exoskeletons of these organisms now so long extinct appear in the rock, differing not in appearance from the shed skin of a Limulus buried in the sand today. We must be filled with awe and with the profoundest admiration for the marvellous ways of nature, when we look upon these remains unchanged in chemical or physical characters during all the aeons which have passed since they were entombed, still retaining the brown color so familiar in modern horseshoe crabs, with the very chitin of the test unimpaired, while even the brittle exoskeleton itself, at times, can be removed from the rock intact.
 Fig. 13. Sketch Map of Oesel for Upper Siluric Localities |
History of Discoveries. This fauna was discovered in 1852 by Dr. Alexander Schrenk, during a trip made for the purpose of studying the Ordovicic and Siluric rocks of the northwest provinces of Russia, namely, Livland and Estland, and of the adjoining islands Oesel, Dago, Moon, Worms, etc. On the first and largest of these islands he found outcrops of the uppermost Siluric rocks in the town of Rootziküll (see map, fig. 13) and there he came upon the first of
