312 THE POST-CBETACEOCTS OF SOTJTHEKN NIGERIA. [Aug. I907, 



or an early deposit of the Cross Eiver I have no means of deciding. A 

 short distance below Itu (Cretaceous) the Benin Sands are lost. 



(d) The Ijebu District. 



In the Ijebu district we find that the Benin Sands and Clays are 

 the most prominent deposits. They are underlain, possibly with a 

 slight unconformity, by a variable group of sands and clays, often 

 impregnated with bitumen, which has permeated the beds according 

 to their interstitial capacity and but rarely taken the form of dykes. 

 From fragmentary fossil evidence, they appear to have been deposited 

 in estuarine or fresh waters. 



As these beds were investigated almost entirely by bore-holes, 

 I feel considerable diffidence in speaking of their fossil contents, but 

 now and again shells have been brought up in the cores. The 

 fossils consist almost entirely of unrecognizable lamellibranchs, but 

 Mr. Henry Woods has kindly identified for me a Natica and a 

 small shell (Meretrisc ?). At one small section north of the little 

 village of Aiye, about 2 j days' journey south of Ondo (say 40 miles), 

 the impressions of shells were found in a bluish-grey clay, overlain 

 by the usual Benin Sands. The clay was so soft and water-logged, 

 that it was almost impossible to preserve the specimens ; but, 

 among the very imperfect impressions brought home, Mr. Woods 

 notes Cardium(?), Arca(?), Astai*te(?), and Gari (Psammobia?). 



So far as can be inferred from the borings, the dip of these 

 beds, taken as a whole, does not exceed 2° or 3° in a southerly 

 direction ; locally, the higher beds at least are false-bedded. 

 Obscure remains of plants are found in other localities. 



It is of interest to record that one section which I examined on 

 the Ogun River, south of Abeokuta, 1 showed about 150 feet of red 

 sandstone (correlated with the Benin Sands) sufficiently compacted 

 to stand as a vertical face ; the rock locally was pebbly, but the 

 quartz-grains were typically angular, variations in coarseness of 

 grain showing the bedding, which, however, was far from marked. 

 Below this section, and a short distance down stream, mauve or 

 whitish clays cropped out. 



These sands and clays are underlain (whether conformably or 

 not, could not be determined at the time) by brown and grey 

 carbonaceous shales, occasionally containing plant-remains in such 

 abundance as to constitute practically a lignite. These beds may be 

 provisionally correlated with the Lignite Series of Asaba, and have, 

 of course, an important bearing on the economic geology of the Colony. 



Additional work in the neighbourhood of Itori would doubtless 

 prove the existence of rocks other than the Benin Sands. About 

 4 miles south of Abeokuta gneisses of various kinds begin, some 

 being markedly porphyritic; and, certainly along the railway to 

 Ibadan, any outliers of the sedimentary series are soon left behind. 



I understand that at Shagamo shale-outcrops are abundant, and 

 from native information I have little doubt that crystalline rocks 

 appear at Ajabamedele on the Oni Kiver, so that the southern 

 boundary of the crystalline rocks is, all things considered, fairly 

 well established. 



1 ' Southern Nigeria Government Gazette' vol. i (1906) no. 10, p. 170. 



