JdO Proceedings of the British Association for [Sept. 



in these calcareous rocks are, in general, the same as those 

 found in England. 



This limestone is succeeded by the coal formation . The 

 newer secondary strata only occur in the north of Ireland, 

 where we have the new red sandstone, with gypsum and 

 beds of magnesian limestone, and these rocks are succeeded 

 by lias, oolite, and chalk. 



2. Dr. West afterwards read an able paper on the geo- 

 graphy of South Greenland. 



Tuesday, Wth. — 3. The Rev. Archdeacon Verschoyle read 

 an interesting paper on a series of trap dykes which occur 

 in the counties of Mayo and Sligo. 



These dykes are remarkable for the length and distinct- 

 ness of their course. Their elevation is E. k W. They 

 are, consequently, parallel to each other, and one of them 

 has been traced for a distance of forty-five miles. These 

 dykes, during this long course, intersect a great variety of 

 rocks, as slate, sand-stone, limestone, mica, and slate, &c., 

 and here produced many curious changes, converting the 

 sandstone into quartz, and even giving it a columnar form. 

 It was the opinion of the Reverend gentleman, that these 

 veins, or a series of them, extended across the island. Mr. 

 Griffith here remarked, that beween Dundrum and Dun- 

 da,lk, on the opposite side of the island, a great number of 

 trap veins had been observed. 



4. Professor John Phillips next read a paper on the fossil 

 Astacidae. 



The speaker commenced by making some remarks on the 

 natural history of the genus Astacus. Of the species which 

 compose the genus Astacus, as at present existing, some are 

 found in salt and others in fresh water. There are two 

 empiric characters by which the marine may be distinguished 

 from the fluveatile Astaci : In the marine species the lateral 

 divisions of the tail are transversely divided, while in the 

 fresh water species the division is longitudinal. The marine 

 species have also large didactylous claws to the first pair 

 of feet. 



All the fossil species possess those characters which be- 

 long to the marine division. Proceeding to investigate the 

 question as to the possibility of identifying strata by means 

 of their organic remains, it was remarked that the study of 



