THE AGE OF INVERTEBRATES OF THE SEA. 47 



itselt partly of organic origin, by that strange process of de- 

 composition or dissolution of foraminiferal ooze and volcanic 

 fragments, going on in the depths of the modern ocean, and 

 described by Dr. Wyville Thomson as occurring over large 

 areas in the South Pacific. The species are two Lingidellic, a 

 Discina and a Leperditia. Supposing these to be all, it is re- 

 markable that we have no Protozoa or Corals or Echinoderms, 

 and that the types of Brachiopods and Crustaceans are of com- 

 paratively modern affinities. Passing upward through another 

 1,000 feet of barren sandstone, we reach a zone in which no 

 less than five genera of Trilobites are found, along with Ptero- 

 pods and a sponge. Thus it is that life comes in at the base 

 of the Cambrian in Wales, and it may be regarded as a fair 

 specimen of the facts as they appear in the earlier fossiliferous 

 beds succeeding the Laurentian. Taking the first of these 

 groups of fossils, we may recognise in the Leperditia a two- 

 valved Crustacean closely allied to forms still living in the seas 

 and fresh waters. The Lingulellae, whether we regard them as 

 molluscoids, or, with Professor Morse, as singularly specialised 

 worms, represent a peculiar and distinct type, handed down, 

 through all the vicissitudes of the geological ages, to the pre- 

 sent day. The Pteropods and the sponge are very similar to 

 forms now living. The Trilobites are an extinct group, but 

 closely allied to some modern Crustaceans. Had the pri- 

 mordial life begun with species altogether inscrutable and 

 unexampled in succeeding ages, this would no doubt have 

 been mysterious ; but next to this is the mystery ot the oldest 

 fc-ms of life being also among the pewest. Whatever the 

 origin of these creatures, they represent families which have 

 endured till now in the struggle for existence without either 

 elevation or degradation. Yet, though thus vast in their 

 duration, they seem to have swarmed in together and in great 

 numbers, in the Cambrian, without any previous preparation. 

 From the Cambrian onward, throughout the whole Palaeozoic, 

 there is no decided break in the continuity of marine life ; and 



