148 Mr Le Huiite on the Geology of 



where these abound, it has a striking resemblance to the older 

 chlorite slate. 



The geology of Wales, and that of the lake district, throw much 

 light on each other, and should be studied together ; but the geo- 

 logist must use the now-neglected crucible as well as the hammer. 

 These two regions afford excellent opportunities of ascertaining 

 the origin of slate, which appears often to be connected with 

 volcanic rocks. In both the variety of the latter is consider- 

 able, while their colours, and apparently their composition, 

 are frequently similar to those of the slates ; so that the nature 

 of their connexion might probably be ascertained by chemical 

 analysis added to attentive observation. I met a black slate in 

 Wales containing numerous crystals, apparently of felspar, but 

 soft, opaque, and partaking in the slaty structure. A yellow 

 slate, well worthy of attention, containing concretions, occasion- 

 ally crystals of hornblende, is found near Festiniog; but it ap- 

 pears to be metamorphic. Besides the various characters im- 

 pressed on the Welsh rocks by the causes already mentioned, 

 there can be no doubt that they have, very generally, been al- 

 tered by heat long after their formation ; to which case geo- 

 logists, I believe, confine the term metamorphic. The frequent 

 proofs that he discovers of this fact may lead an inexperienced 

 geologist, as it led me for some time, to attribute all the pheno- 

 mena that I have noticed to this cause alone ; and, if disposed 

 to theorize, he may form various ingenious and plausible con- 

 jectures as to the origin of these rocks, whether in beds or pro- 

 truded masses, whose claims to the title of pyrogenous appear 

 doubtful. Such conjectures would receive some support from 

 the fact, that we find, in the same district, rocks decidedly of 

 aqueous origin, similar in composition, and often in some of 

 their other characters, to the more remarkable of those whose 

 origin may be considered doubtful. The two slates last no- 

 ticed afford examples of this; and near Festiniog others maybe 

 seen. My space, however, forbids me to say more on this sub- 

 ject ; but I cannot leave North Wales, without noticing another 

 of its rocks. The coarse sandstones and conglomerates, which 

 we there so frequently meet, often exhibit proofs of haying been 

 in a soft state ; but whether they are concretionary, or have 

 been softened by heat, is not easily determined. In general, 



