MONIAN SYSTEM OF EOCES. 



519 



m 



^1 



by two or three bands of more earthy limestone, and there arc often 

 two or three grains within another grain. In fact, larger fragments 

 of the rock with several scattered grains may themselves be coated 

 with earthy limestone, and be imbedded in a more crystalline matrix. 

 Such material forms a very consider- 

 able portion of the rock. We can 

 understand its formation by the ac- 

 tion of calcareous springs, which first 

 deposit, then break up and roll the 

 fragments, and coat them with cal- 



careous matter. Such oolites are 

 formed by the calcareous springs of ^ 

 the Solfatara, and I can conceive of ^• 

 no other origin for these limestones. g 

 They are obviously subsequent to the o 

 ashes. ? 



The next promontory, forming the 

 eastern face of Ogo-gyfwr, brings us to 

 to the summit of the series and in- oj 

 troduces the overlying rocks, which, £. 

 though they have not been searched 

 for fossils, we may recognize as the 

 Ordovician as soon as the basement- ^ , 

 beds have given place to slates. By >- 

 climbing down the face of the cliff |' 

 and clambering over the rocky ledges 

 the following section (fig. 21) may be 

 examined bed by bed. Here the ashes -"^ 

 on the south are nearly vertical, and o^ 

 finish off by an infusion of quartz o^ 

 against a strong fault now indicated | 

 by a slanting cave. On the north | 

 side of this fault we find horizontally S" 

 undulating conglomerates lying on 

 well-bedded quartzose rocks of the ^ 

 ashy group, and terminating against * 

 the fault. The lowest conglomerate ^ 

 is of small pebbles; above this are ^ 

 variable grits, and then a larger |' 

 conglomerate. After an interesting ?' 

 interruption in the shape of a pair 

 of trough-faults letting in a syncli- <. 



nally disposed slice of black slates 

 resting on a coarse conglomerate, 

 the series is continued upwards by a ^ 



mass of black slates continuing for 



some distance, and finally appears another band of conglomerate. 

 Here the sequence of these rocks ends, and their place is taken by 

 contorted slaty rocks of the older group which become gradually 

 calcareous, and pass into the familiar limestone. We thus assume 



f 



