158 J. Starliie Gardner — Development of Dicotyledons. 



In Bulletin No. 30, Mr. Walcott treats mainly of the fauna of the 

 Middle Cambrian rocks and figures and descriptions of a large 

 number of new genera and species are given. In Great Britain the 

 fauna of these rocks is comparatively a poor one, and none of the 

 typical American forms have as yet been discovered in them. 



The American Middle Cambrian fauna is said to combine ' " the 

 characters of the Lower Cambrian and Upper Cambrian faunas and 

 yet is distinct from each of them. . . . The conditions that developed 

 the Middle Cambrian fauna appear to have been largely peculiar to 

 the American continent. During the deposition of the St. John's 

 series of the Lower Cambrian, or the Paradoxides strata, we learn 

 from the European and eastern American sections, that the fauna was 

 essentially of the same type over the entire basin (Atlantic), and, 

 from evidence known to date, that the fauna did not extend west of 

 a line passing north-east through Eastern Massachusetts to New 

 Brunswick and Newfoundland. . . . From the data we now have, I 

 think that during the existence of the greater portion of the Lower 

 Cambrian (Paradoxides) fauna, a barrier existed that prevented its 

 extension westward of the line mentioned ; that towards the close of 

 the time of the Paradoxides fauna that barrier was removed to the 

 north-east, in the vicinity of Newfoundland, and the descendants 

 from the Paradoxides fauna entered the westward seas and spread to 

 the eastern and western basins and formed the Middle Cambrian 

 fauna. What route was taken by the Middle Cambrian fauna after 

 passing to the western side of the outer barrier is not yet traced, but 

 I think from the indications we now have of a continental area, 

 during Lower and Middle Cambrian time, in the central portion of 

 the continent, that the fauna passed to the south around the southern 

 end of the then existing land, and thence north along the west shore. 

 In the Atlantic basin, the Paradoxides fauna persisted to a greater or 

 less extent and mingled with the types of the Upper Cambrian fauna, 

 as in the Upper Lingula Flags of Wales." 



As Mr. Walcott is personally acquainted with the strata from which 

 the fossils have been obtained, and has studied in the field most of 

 the sections referred to, the conclusions at which he has arrived 

 are important and highly deserving of very thoughtful consideration. 



V. — The Appearance and Development of Dicotyledons in Time. 

 By J. Starkib Gardner, F.G.S., F.L.S. 



IT has been acknowledged by botanists that the methods generally 

 pursued in determining fossil dicotyledonous plants have been 

 scarcely such as were likely to lead to trustworthy results. Their 

 study has, or should have, two practical aims. The one, that geo- 

 logists may be able to determine the ages of strata, when they only 

 contain fossil plants, with as much certainty as if they contained the 

 remains of animals. The other, that botanists may be able to trace 

 the evolution of the existing genera of plants from the palseon to- 

 logical record under conditions no less favourable than those at the 

 disposal of the zoologist. 



1 American Journal of Science, toI. xsxii. p. 181. 



