370 Scientific Intelligence. 



II. Geology. 



1. La Flora Liasica de la Mlxteca Alia ; by G. R. Wielakd. 

 Boletin del Institute Geologieo <le Mexico, No. .31. Text of 

 VI + 165 pp. quarto (Mexico, 1914); Atlas of 24 pp. and 50 

 plates (dated 1910).— This is the first typical North American 

 Liassic flora. It was collected in entirety by the writer in the 

 winter of 1909. Its age was discussed in this Journal for Septem- 

 ber 1913 (vol. xxxvi, pp. 251-281). Evidently the "Mixteca 

 Alta" of Oaxaca, Guerrero, and Puebla is one of tbe richest 

 Cycadeoid regions in tbe world. Neither tbe Yorkshire coast nor 

 tbe Gondwanas of India surpass tbe new Mexican realm in any 

 respect. 



The main collections described are from the Barranca Consuelo 

 in tbe western part of tbe state of Oaxaca. The section bere 

 measured includes 600 meters of plant-beds resting on an eruptive 

 floor, and followed by a marine Jurassic series. The measure- 

 ments were continued upward through tbe marine superposition 

 about 375 meters to the base of the Cretaceous. The study of 

 these superposed beds has not been completed by any one and 

 was excluded from the field investigated. Taken as a whole the 

 Consuelo section must always rank as one of the most important 

 type sections of the North American continent. 



The plant-beds consist in a much varied succession of shahs 

 and sandstones grading into finer conglomerates. Occasionally 

 the finer shales carry coal. In the lower beds seams of a semi- 

 anthracite with a high ash recall the coal of Sutherlandshire, 

 Scotland. An equivalent of the Sonoran Trias was not positively 

 determined, but may occur in the valley of the Rio Nochixtlan. 

 If true Rhretic is present at the base of tbe Consuelo section the 

 fact was not determined. The section readily divides itself into 

 a lower series 250 meters thick and an upper series 300 meters 

 thick ; but no unconformity was observed. In the collections 

 secured the cycads and ferns are relatively modern. The suc- 

 cession of plant types precludes any notable time gap. The 

 Rhsetic and the Oolite must afford the extreme boundaries. 



The discovery of Cordaiteans (N^rer/gerathiopsis) closely asso- 

 ciated with Liassic Cycadeoids (Otozamites) was unexpected. 

 The handsome plates of the Atlas show various new William- 

 sonian fronds and a fine series of fruits. Yet these must be but a 

 mere fraction of the recoverable forms. Of the 70 or more plant 

 types illustrated or described, a considerable number so closely 

 resemble plants of the European Liassic that new varietal names 

 only are attached. It is, however, likely that Professor Nathorst, 

 who takes exception to this method in a recent letter, is justified. 

 He thinks far separated plants nearly always likely to be of dif- 

 ferent species, while varieties even if present can rarely be deter- 

 mined. 



