10 GEOLOGICAL MEMOIRS. 



which belong to the Mastodon angustidens. In this collection there 

 are also some species of vertebrata not hitherto known to occur in 

 that place, and the first specimen which I saw in the rich collection 

 of Professor van Breda was a new rodent from Oningen, to which I 

 have given the name of Sciurus Bredai. In Tayler's museum I saw 

 also the Anguisaurus from the lithographic slates of Solenhofen, 

 assuredly a most remarkable creature and well deserving a thorough 

 description, which however would require more time than I can com- 

 mand. It seems related to the Pleurosaurus, of which I have the 

 middle portion of the skeleton before me, and perhaps the two genera 

 may come to be united. 



Whilst residing on the coast of the North Sea in Holland and 

 Belgium, I thought myself transported to the very workshop where 

 the marine molasse and the shell-sandstone of the molasse were form- 

 ing before my eyes. The dunes are an analogous formation ; the 

 sand of the dunes is the molasse sand of historical times ; the simi- 

 larity is so remarkable that it only requires consolidation, in order to 

 represent the molasse sandstone with its contents, which v»^ould con- 

 sist of living instead of extinct species. The sand of the dunes rarely 

 envelopes mollusks in a living state ; it is chiefly the shells of dead 

 animals, and these for the most part fractured, broken into frag- 

 ments or rubbed by the incessant beating of the waves. The beach, 

 seen during the ebb, may be compared to a great extent of exposed 

 strata, on which remains of organisms appear in various places. 

 Even the flame-like distribution of colours and other markings on 

 the divisional surfaces of rocks may be partly explained by the de- 

 posit of foam from the waves. The manner in which the waves 

 during the ebb of the retiring sea sport with the fine sand on the 

 beach is very interesting. They give it a wave-like, variously fur- 

 rowed arrangement, resembling the sculptured markings on the skull 

 of the crocodile. Similar appearances, and no less regular, occur on 

 the surfaces of many rocks containing petrifactions. The sea-shore 

 may also convince us that many phsenomena in the fossiliferous 

 rocks have their cause in the alternation of the seasons, — a phsenome- 

 non which must be carried further back in the history of the earth 

 than our theorists imagine. When it is considered for example that 

 the immense profusion of fish on the shores of the Netherlands, in 

 summer declines to absolute poverty, many of the fish then seeking 

 other littoral regions, we may conceive that the variation in the 

 numbers of petrifactions which the strata of one and the same for- 

 mation present, the alternation of highly fossiliferous beds with others 

 in which fossils are rare or entirely wanting, that the interruptions 

 in the occurrence of species by beds in which they do not appear, as 

 well as the diversity in fossils which is observed when in wide-spread 

 formations the same stratum is followed to distant points, may in part 

 be explained by the alternation of seasons. On the strand, newly ex- 

 posed by the retiring sea, at the season of my visiting it, I rarely found 

 a fish ; it was chiefly mollusks, sea-stars, among them often those with 

 four rays, prawns, and among plants fucoids, that were left behind. 

 In a sand-hill I found the shell of a crab full of the fine sand, and in 



