132 



LAMARCK, HIS LIFE AND WORK 



Hence there have been changes of climate since 

 these forms flourished, and, he adds, the intervals 

 between these changes of climate were, stationary- 

 periods, whose duration was practically without 

 limit. He assigns a duration to these station- 

 In i66g, in his treatise entitled De Solido intra Solidum naturaliter 

 contento, which Lyell translates "On gems, crystals, and organic 

 petrefactions inclosed within solid rocks," he showed, by dissecting a 

 shark from the Mediterranean, that certain fossil teeth found in Tus- 

 cany were also those of some shark. " He had also compared the 

 shells discovered in the Italian strata with living species, pointed out 

 their resemblance, and traced the various gradations from shells merely 

 calcined, or which had only lost their animal gluten, to those petre- 

 factions in which there was a perfect substitution of stony matter" 

 (Lyell's Principles, p. 25). About twenty years afterwards, the 

 English philosopher Robert Hooke, in a discourse on earthquakes, 

 written in l588, but published posthumously in 1705, was aware that 

 the fossil ammonites, nautili, and many other shells and fossil skeletons 

 found in England, were of different species from any then known ; but 

 he doubted whether the species had become extinct, observing that 

 the knowledge of naturalists of all the marine species, especially 

 those inhabiting the deep sea, was very deficient. In some parts of his 

 writings, however, he leans to the opinion that species had been lost. 

 Some species, he observes with great sagacity, "are peculiar to certain 

 places, and not to be found elsewhere." Turtles and such large 

 ammonites as are found in Portland seem to have been the productions 

 of hotter countries, and he thought that England once lay under the 

 sea within the torrid zone (Lyell's Principles^. 



Gesner the botanist, of Zurich, also published in 1758 an excellent 

 treatise on petrefactions and the changes of the earth which they 

 testify. He observed that some fossils, "such as ammonites, 

 gryphites, belemnites, and other shells, are either of unknown species 

 or found only in the Indian and other distant seas " (Lyell's Principles). 



Geikie estimates very highly Guettard's labors in pala;ontology, say- 

 ing that " his descriptions and excellent drawings entitle him to rank 

 as the first great leader of the palaeontological school of France." He 

 published many long and elaborate memoirs containing brief de- 

 scriptions, but without specific names, and figured some hundreds of 

 fossil shells. He was the first to recognize trilobites (Iltenus) in the 

 Silurian slates of Angers, in a memoir published in 1762. Some of 

 his generic names, says Geikie, " have passed into the languages of 

 modern palasontology, and one of the genera of chalk sponges which 

 he described has been named after him, Guettardia. In his memoir 

 " On the accidents that have befallen fossil shells compared with those 

 which are found to happen to shells now living in the sea" (Trans. 

 Acad. Roy. Sciences, 1765, pp. 189, 329, 399) he shows that the 



