Kvamshestens devonfelt. 79 



paa devontidens saakaldte røde fastland, og da vilde det være 

 limelig at anta at ialfald endel av de betydelige masser av sten 

 som nu findes i de undre breksier og konglomerater ved vældige 

 og sjeldne regnstrømmer, som vi kjender dem fra ørkener og ørken- 

 lignende strøk, fra dalsidene er bragt ned i bækkenene. 



En sammenligning med forholdene som de antas at ha 

 været i devontiden i Skotland vil ha sin interesse. 



Om de klimatiske forhold i begyndelsen av Old Red tiden 

 finder vi i det i 1914 utkomne arbeide »The Geology of 

 Caithness« av C B. Crampton og R. G. Carruthers m. fl. 

 følgende bemerkning: »The climate of the Lower Old Red 

 Sandstone times was sufficiently humid to lead to intense 

 erosion and rounding of the fragments of hard crystalline 

 rocks by stream action.« »The red colours of the rocks 

 and the predominantly decomposed state of the felspars of the 

 Caledonian deposits therefore points to a climate which was not 

 only humid but warm.« 



Om forholdene i begyndelsen av Middle Old Red tiden er i 

 samme avhandling anført: »The mudstones and arkoses are still 

 red like those of the Caledonian but the coarser deposits are of 

 less extent and different in nature. The breccias consist of very 

 angular and fresh fragments and the conglomerates are full of 

 fragile plate-like pieces of shist and subangular boulders, sugge- 

 sting that transport by water had ceased to be so marked a feature. 

 The red colour of the mudstones shows that the climate remained 

 warm, but the fresh and angular fragments of crystalline rocks 

 in the breccias and arkoses suggest a change to more arid 

 conditions. 



With the advent of flagstone formation the red colour disap- 

 pears from the rocks. — Goodchild considered the absence of 

 a red colour in the Caithness flagstones as due to the excess of 

 organic matter. The iron is reduced to ferroso-ferric and fer- 

 rous compounds. 



The appearance of so much organic matter is not to be accoun- 

 ted for by a change to a cold humid climate since red 

 rocks reappear at several horizons in the middle of the flag- 

 stone sequence, the disappearance of the red colour in the rocks 

 can be explained as the direct outcome of the change in the condi- 

 tions of sedimentation which introduced organic matter into the 



