THE LAMELLIBRANCHS OF THE SILURIAN ROCKS OF GIRVAN. 



481 



is a great development of coarse sediments, consisting of conglomerates, grits, 

 greywackes, flagstones, mudstones, and shales, implying deposition near land and in 

 comparatively shallow water. As might be expected from the foregoing conditions, 

 the Girvan series yields organic remains in profusion, on certain horizons. Of special 

 importance are the bands of graptolite shales, yielding many of the zonal forms of 

 the Moffat region which enabled Professor Lapworth to correlate the Silurian divisions 

 of the Girvan and Moffat areas. 



Table of Silurian Strata, Girvan. 



E. F. 



Tarannon. Wenlock. 



1 . Blair and Straiton Beds. — Grits, flags, and shales. Beyrichia Klvedeni . 



Thickness. 

 500 feet. 



2. Drumyork Flags, Bargany Group. — Shales, etc. Gyrtograptus Grayi, 

 Monograptus priodon ......... 



1. Penkhill Group. — Grits, purple shales. Monograptus exiguus, Crossopodia 



1100 feet. 

 1000 feet. 



D. 

 Llandovery. 



3. Camregan Group. — Grits, limestones, shales. Rastrites maximus, 

 Pentamerus ........... 



2. Saugh Hill Group. — Flagstones, shales. Monograptus spinigerus, 

 Rastrites peregrinus ......... 



1. Mulloch Hill Group. — Conglomerate, sandstone, shales. Diplograptus 

 acuminatus, Meristella ......... 



200 feet. 

 500 feet. 

 350 feet. 



C. 



Caradoc. 



Ardmillan Series. 



5. Drummuck Group. — Mudstones, with Star-fish beds on top. Dicello- 



graptus anceps, Trinudeus ........ 



4. Barren Flagstone Group. — Diplograptus {Orthograptus) truncatus, 



Nematolites ........... 



3. Whitehouse Group. — Dicellograptus, Pleurograptus, trilobites 



2. Ardwell Group. — Flagstones, shales. Climacograptus caudatus, 



Dicranograptus .......... 



1. Balclatchie Group. — Mudstones, conglomerate. Glimaeograptus bicornis. 



Fossils abundant .......... 



400 feet. 



800 feet. 

 300 feet. 



1200 feet. 



100 feet. 



B. 



Llandeilo Area, N. 

 of Stinchar. 



Barr Series. 



4. Benan Conglomerate .......... 



3. Graptolitic Mudstones. — Didymograptus superstes . .... 



2. Stinchar Limestone. — Trilobites, brachiopods, corals .... 



1. Kirkland Group. — Sandstones, conglomerate. Orthis confinis. Local 

 unconformability . 



500 feet. 

 30 feet. 

 60 feet. 



240 feet. 



A. 

 Arenig. 



3. Radiolarian Cherts, mudstones, volcanic tuffs, Arenig and Lower 



2. Bennane Head Black Shales. — Interleaved with volcanic agglomerate. 

 Tetragraptus bryonoides ......... 



1. Volcanic rocks, lavas, tuffs, with fossiliferous intercalations Approxi- 

 mate thickness .......... 



Base not seen. 



70 feet. 



3-4 feet. 



1500 feet. 





