564 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



but is always on a small scale. Higher still occur massive beds which 

 show little bedding, but are characterized by a vertical flaking. At the 

 top of this are the brecciated layers. 



About 125 feet above the conglomerate, at the top of the first cliff, 

 back of the shore cliff, is an exceedingly irregular line of contact between 

 dolomitic calcarenites and the overlying calcilutites. The following 

 sketch from my notes shows this contact as exposed on a part of the cliff. 



It is difficult to decide whether this is a sedimentary contact or repre- 

 sents irregularity of dolomitization of the limestones. The appearance 

 in some cases suggests irregular ridges of dolomite, comparable to the 

 "yardangs" of central Asia, as described by Sven Hedin. 7 The spaces 



Figure 2. — Irregular Contact between Dolomite and bedded Caleilutite in the Cliffs 

 facing the Kyle of Durness, Scotland 



This may represent the Cambro-Ordovicic disconformity 



between the ridges are filled with fine, stratified lime mud. This often 

 shows brecciation, and fragments of dolomite are frequently included in 

 the limestone, resembling broken-off masses. 



Somewhat higher begin the beds of the Sailmhor group, which com- 

 prise for the most part strongly mottled dolomites, to which the local 

 name, leopard stone, is applied. The rock has the appearance of a brec- 

 cia composed of dark and light angular fragments. The brecciation is 

 probably the result of dolomitization. Much chert is present, but the 

 rock as a whole shows little evidence of stratification. This rock has 

 furnished the following fossils : 8 



1. Isotelites canalis (?) Conrad. 



2. Murchisonia sp. 



3. Pleurotomaria (Euconia) etna Bill. 



4. P. (Euconia) ramsayi Bill. 



5. Cyrtoceras, two species. 



6. Orthoceras sp. 



7 See illustration reproduced in my Principles of Stratigraphy, p. 53, fig. 13. 



8 Peach and Home : Loc. cit., p. 629. 



