164 GEOLOGY AXD PETROGRAPHY OP CLARENCETOWN-PATERSON DISTRICT, i., 



rocks," but on account of a subordinate content of fragmental material should 

 be termed tuffaceous rhyolites, tuffaceous toscanites and so on. Then, it would 

 be scai-cely feasible, in a section such as the Langlands Section (Text-fig. 3), to 

 postulate that the massive rocks are intrusive, on account of the very small in- 

 terval separating one horizon from the other, the absolute absence of transgression, 

 and the apparent absence of contact metamorphism or the visible effects of mar- 

 ginal assimilation which might reasonably be expected from such acid rocks. 



Thus the only horizons about which any doubt remains are the more basic 

 and those which elsewhere in the State appear to be sometimes definitely intru- 

 sive and which, in the area under consideration, are not accompanied by tuffs 

 of similar composition. 



A number of exposures of the hornblende-andesite show its junction with the 

 adjacent sediments, and no signs of intrusion are in evidence. The thickness of 

 tliis unit varies abruptly from point to point, and the change is in direct sym- 

 pathy with the variation in the degree of development evidenced by the volcanic 

 series as a whole. The hypersthene-andesite and andesitic pitchstone also give 

 no indication of an intrusive nature where junctions with adjacent strata are 

 observed. 



The Burindi Series. 



A considerable amount of difficulty is experienced in determining the de- 

 tailed succession in the Burindi Series, owing to the lack of persistent horizons 

 and the complexity brought about by faulting. 



Some idea of the chief features of the lower portion (in a comparative sense) 

 of the rocks of the Hilldale district has been obtained. At this locality the beds 

 are developed in a plunging anticline which pitches to the south-south-east and, 

 as one proceeds north-east, the mudstones which outcrop in portion 100, Parish 

 of Barford, and form the lowest beds lexposed, are followed by red gi'itty tuffs, 

 which outcrop very poorly for a considerable distance and appear to pass into 

 slightly different tuffs, which are more acid and mica-bearing and form a mass 

 about 500 feet thick, in turn passing into the Basal Stage of the Kuttung Series. 

 On the south-western side of the anticlinal axis a better section is seen and, 

 proceeding upward stratigraphically, we have : 



(i.) Green Mudstones and Shales 40 feet 



(ii.) Impure Limestones with marine fossils 70 „ 



(iii.) Fine-grained Tuffs with fossils .... 25 ' ,, 



(iv.) Medium-grained Tuffs containing jasperoid frag- 

 ments 20 



(v.) Shales or fine TuiTs 20 „ 



(vi.) Coarse Tuffs 80 „ 



(vii.) Mudstones 30 „ 



Total Thickness 2S.5 „ 



The mudstones (i.) and (vii.) are those characteristic of the Burindi Series, 

 and contain quite a quantity of indeterminate plant remains. The limestones 

 are made impure by quite a large proportion of tuff, in places passing into tuffs. 

 On account of the conditions which obtained during the accumulation of the 

 coarse material which helps to make up the limestones, many of the fossils are 

 only imperfectly preserved. This horizon, together with the next (iii.) which is 

 characterised by an abundance of the remains of Orthis nesupinata, forms a 

 well-known hunting gi-ound for fossil collectors; crinoid calyxes have often been 

 found, but the state of preservation is such that the identification of many is 

 unfortunately impossible. 



