568 Reviews — Geological Survey of IreLnd. 



the proximity of the great mass of granite, especially as they appear 

 to he intercalated with nodular and calcareous schists, etc. 



With reference to the conclusions (p. 15) arrived at, we must 

 confess that we have found great difficulty in understanding the pre- 

 cise meaning of the author, especially with regard to his explana- 

 tion of the ages of the various igneous rocks, since it is difficult to 

 reconcile statements in the various paragraphs (p. 15) which never- 

 theless may be clearer in the mind of the writer. It is, however, 

 suggested by Mr. Kinahan that the sedimentary rocks which are now 

 metamorphose, previous to that action taking place, were the oldest 

 in the district ; that they were invaded by what are now the me- 

 tamorphose homblendic and felspathic intrusive rocks, and after- 

 wards all were affected by the granite, which action ceased after 

 the intrusive granite had been formed ; and, at a still more recent 

 period, the country was cut up by dykes of the more modern 

 intrusive rocks (p. 15). 



In perusing the remarks (pp. 16, 17) on "the supposed meta- 

 morphic eruptive rocks," and the mode of accounting for their 

 modifications, we regard the evidence advanced in favour of his 

 views as far from satisfactory, and somewhat tending to the 

 doctrine of transmutation, too often so great a favourite with field 

 geologists, especially when (p. 17) the disappearance, or alteration 

 in appearance of the hornblendic rocks, by their " being incorporated 

 in the granite " is spoken of, forgetting that there are serious ob- 

 jections, in a chemical point of view, to the acceptance of such a 

 theory. 



Mr. Kinahan, however, observes " that in the Porphyritic granite 

 there are tracts in which hornblende, sphene, chlorite, and epidote, 

 separately or combined, seem to become essentials of that rock ; and 

 is it not possible that such places point to localities in which hom- 

 blendic igneous rocks originally existed ?" 



Throughout the paper, many terms are made use of which are 

 certainly objectionable as conveying somewhat indefinite meanings, 

 such as tracts, courses, pipes, flying dykes, porphyries, etc., and in a 

 petrological paper, we should expect the mineral species to be more 

 exactly defined, and not for example to find a mineral described as 

 "perhaps an earthy chlorite," whatever that may be. 



The aqueous rocks and the relations between the form of the 

 ground and its internal structure are subsequently noticed. The 

 latter, an important and highly useful portion of all geological 

 descriptions, we are glad to remark generally, if not always, finds a 

 place in the ' Explanations ' of the sheets of the Irish Survey. 



The detailed descriptions as to the position and lie of the rocks, 

 occupy the chief part of the Memoir, and evince a vast amount of 

 labour on the part of the author, abounding as they do in carefully 

 I'ecorded facts, and many suggestive remarks well worthy the atten- 

 tion of the reader, both as to the mineralization and metamorphism 

 the various rocks have undergone at difierent times, and as to the 

 origin of the nodular and crumpled foliation in the metamorphic 

 sedimentary rocks. The area described is divided into six districts, 



