But, beside these, there have been discovered in the silurian rocks six or seven genera, involving a still greater number of species, of fishes of the order of the Placoids, so denominated from the broad scales or plates with which they are covered. The probability is, that more of these higher organisms will yet be brought to light, as all the strata of the system consist of marine deposits, and only the most limited sections have anywhere been explored. They constitute the lowest of the fossiliferous beds; are generally found, except in Russia, in a vertical or highly inclined position, and consequently but little of their superficial area is exposed. Here, however, geologists have named and described an Onchus Murchisoni, a Thelodus parvidens, and other four genera of equally erudite-sounding names. The onchus type is continued, and greatly multiplied in species, in the two succeeding formations, when it dies out, or at least no trace of the genus is found in later times; while the rest appear to come and to depart within their own geological epoch. These organisms are all as yet termed Ichthyolites, that is, simply fossil fragments of fish, as no entire animal has been anywhere detected, while of their true class M. Agassiz affirms with confidence. Teeth, fins, spines, occur so abundantly in a stratum of the Upper Ludlow series in Wales as now to be termed “the bone-bed,” giving assurance that the seas were thus early stocked with the finny tribes. The families of most of these fishes have yet to be determined. But nature, though in her operations “simpler than man’s wit would make her,” was still pretending enough to be shaping out thus early the higher types of life. The science which introduces to such sights and studies, occupies no mean place among the various branches of human inquiry. To neglect to decipher what is so indelibly recorded on these pages of creation, is willfully to shut oneself out from what has been actually preserved for information—a voice from the past, which speaks in the same distinct articulate language as the present of the fiat of Omnipotence. No object is mean or contemptible which divine wisdom has formed, and no subject is unworthy of investigation which illustrates His ways and works during any period of creation.