l8o THE HABITAT OF THE EURYPTERIDA 



Upper Old Red sandstone was deposited over the whole of Scotland. 

 In the words of the two authors mentioned above, "The great mass 

 of this mountain chain, then, must have lain to the northwest of the 

 present Old Red Sandstone area, and we now proceed to show how 

 after this long period of upheaval the mountain mass once more 

 began to sink below the level of the sea, and that gradually the waters 

 of the Old Red Sandstone sea levelled it down to the very core" 

 (159, 109). They consider that all of the deposits were made along 

 shore, but they are then confronted by the problem of the lack of 

 molluscs and other typical marine forms. This absence they thus 

 account for: "The solution of the problem rather lies in the fact that 

 the presence of peroxide of iron in these rocks is inimical to the pre- 

 servation of fossils with a calcareous test, and that more especially 

 in the case of sandstones, which even when composed of pure sand 

 are well known to be a bad medium for the preservation of molluscan 

 and other similar organic remains" (159, 116). 



Objections to Lake and Marine Theories. Each of the two 

 theories given can explain some facts which the other cannot; but, 

 on the other hand, each has very serious faults due in some cases to 

 incorrect observations, in others to the acceptance of prevalent ideas 

 and in others to unjustifiable deductions. Both theories contain 

 elements of truth, but both are open to many objections. These fall 

 into two groups: (1) Physical, (2) Faunal. 



(1) Physical, (a) Red color. Within the last twenty years stu- 

 dents of sedimentation have clearly shown that it is impossible for 

 a widespread and thick series of red clastic deposits to be laid down 

 in the sea. The red color, as is well known, is due to the dehydration 

 of sediments which were thoroughly oxidized at the time of deposi- 

 tion. Such oxidation cannot take place under water, but only during 

 exposure to the air. It is not to be supposed that the beds were red 

 when deposited, but that only after dehydration had taken place 

 by the lapse of a long period of time, or through the effect of heat 

 from the interior of the earth, or by pressure was the red color taken 

 on. Of course, certain red beds may receive their final working over 

 under water, but such deposits will be of limited thickness and areal 

 extent. For instance, the Bays sandstone (Upper Ordovicic) of 

 Tennessee, Virginia and adjoining regions is a red calcareous sand- 

 stone with a maximum thickness of 1500 feet. Throughout most of 

 the formation organic remains are absent, but in the lower beds marine 

 fossils occur abundantly in a few layers of the red sandstones. These 



