Vol. 60.] OF THE EAST-CENTRAL HIGHLANDS. 433 



the sifting-away occasionally takes a stronger form, and large holes 

 were dug in the soft dark mud, one of which occurs at Bilsdale 

 (nearly 100 feet deep), the other near Hosedale Abbey ; in both 

 cases, the eroded hollow was filled up with impure limestone. 



No further evidence, bearing on this investigation, is met with 

 till the northern end of the long straight portion of the Tilt Valley is 

 reached. Here, just above the junction with the An Lochan, a 

 section occurs closely resembling that at the sharp bend in the Tilt 

 at Crombie Wood, below Gilbert's Bridge : the Pink Felspathic 

 material being again present. Ascending the river-bed from this 

 point, when the stream is low, the Honestones can be seen to pass 

 gradually into fine Moine Gneisses. This part of the river is some- 

 what obscured by numerous small protrusions from the Glen-Tilt 

 complex ; but the passage can be well seen a little above Pool Tarf, 

 along the bed of the Tilt, and in the first small stream south 

 of the Tarf. Here, the passage of the Honestones into the Moine 

 Gneisses is practically unbroken. This is due to the lucky accident 

 that only the less markedly-siliceous part of the Honestones is 

 present; a single infold of the more markedly-siliceous portion 

 would have broken the continuity of a gradual change. 



On looking at the map, the reason why this gradual change can 

 be traced becomes at once obvious. As in the Gilbert"s-Bridge 

 section, the Tilt once more makes a large bow. As before, one end 

 of the bow lies at one side of the belt of decreasing alteration, the 

 other almost at the opposite side ; it does not quite do so, and this 

 is why, in addition, the small burn has to be ascended in order to 

 see the full change. 



(h) The Falar Area. 



Considerable light is thrown on the present investigation by the 

 clear, continuous sections in the deep gorges that characterize the 

 Ealar portion of the Tilt drainage-area. The most convenient 

 starting-point lies at the junction of a little burn with Glen llohr, 

 immediately north of Glen Bheag. In the lower part of the little 

 burn, the small sill of hornblende-schist and part of the Dark Schist 

 are exposed, repeated several times by folding. In the bed of the 

 main stream below, is an excellent section of the Honestones with 

 the Little Limestone next them, and beyond this a high bank 

 composed of the Dark Schist. The locality was often visited in 

 former years by farmers and shepherds, who came from considerable 

 distances to procure a certain portion of the parallel-banded material 

 to be used as honestones, and it is to this fact that the beds owe their 

 distinctive name. These Honestones are characterized by their even 

 colour-banding, and are composed of a number of alternating softer 

 and harder layers, most of which contain a considerable amount of 

 biotite, arranged parallel to the banding or bedding. The portion 

 of the rock nearest the Little Limestone is, on the whole, the 

 softest; and it at first contained most clastic chlorite. This often 

 occurred in little felted films, obviously identical originally with the 



