256 



SCIENCE. 



[N. S. Vol. V. No. Ill, 



peated in most countries until Ordovician 

 time. 



Not only are these old Cambrian faunas 

 remarkable for the peculiar types of 

 Brachiopods which they possess, but they 

 are also remarkable for those they lack. A 

 lAngida has not been found, though Lin- 

 gulella is a common genus. 



The larval growths of Ordovician and 

 Silurian Lingula carry us back to a form 

 which is oboloid. Thus in L. quadrata, L. 

 Howleyi, etc., the shell is first circular as in 

 Obolus, then oval as in L. quebecensis, etc., 

 and finally takes on the sub -quadrate form 

 of the adult shell. But there is a more 

 elementary form of the Brachiopod shell 

 than the circular shell of Obolus; this is 

 seen in Paterina and the young shell of 

 Botsjordia, which is nearly semicircular. 

 Both these shells come from beds which are 

 older than Paradoxides. 



Ostracoda. — The Ostracoda also gives us 

 definite forms peculiar to the early Cam- 

 brian beds. Such are the types represented 

 in Beyrichonia and Hipparieharion ; such al- 

 so are those with flexible tests represented 

 by Aluta. Other Ostracods are present in 

 more varied forms than in the Paradoxides 

 beds. 



The distinctive features of the animals 

 of the earliest Cambrian faunas may be 

 summed up as follows : 



1 . The trilobites retain larval character- 

 istics to an unusual degree. 



2. The Brachiopods have a large per- 

 centage of oboloids. 



3. The Ostracoda are plentiful and varied 

 and present some peculiar types. 



Another paper which will probably be of 

 considerable interest in America is Dr. H. 

 J. Johnston-Lavis' criticism on the work of 

 Messrs. Weed and Pirsson on the High- 

 wood Mountains. These writers describe 

 Square Butte as a laccolite formed in Creta- 

 ceous sandstones and composed of an outer 

 and upper layer of a basic rock that they 



name shonhinite, with a core of syenite. The 

 shonkinite shows a laminated structure 

 parallel to the roof, as was likewise the case 

 with the upper part of the syenite. They 

 consider this variation in the rock to show 

 difierentiation by diffusion and separation 

 of the two magmas and that the lamination 

 was due to the isotherms in the cooling 

 mass. Dr. Johnston-Lavis showed that 

 these interpretations were not in accord 

 with the facts ; if such differentiation had 

 occurred, the line of junction of the two 

 rocks should be roughly horizontal and not 

 parallel to the roof, and he suggested tliat 

 the lamination was due to shearing planes. 

 His view was that the shonkinite had been 

 delayed in the volcanic conduit and had 

 been basified by osmotic action between the 

 paste and the limestone or other basic rock- 

 walls. This first filled the laccolite and was 

 followed by the less basic or unaltered syen- 

 ite from below. The white, dyke-like mass 

 was an insuperable difficulty to the views of 

 Messrs. Weed and Pirsson and only expli- 

 cable by the theory of the present author. 



Sir Archibald Geikie read a very inter- 

 esting paper in which he recognized that 

 some rocks previously described as volcanic 

 agglomerates in Anglesey were in reality 

 crush rocks, but a great deal of volcanic 

 material had contributed to their original 

 formation. Mr. Greenly also attributed 

 the quartzite lenticles of the same island 

 to a similar action upon beds of grit and. 

 sandstone. In a second paper he described 

 the occurrence of Sillimanite-Gneisses in 

 Anglesey. The curious mass of ancient 

 rocks which is half submerged under the 

 Trias of eastern England, at Charnwood 

 Forest, was described in some detail by 

 Mr. Watts, who attributed to it aPre-Cam- 

 brian age. He further pointed out that a 

 landscape at least as old as the Trias was 

 here being gradually exposed to-day by the 

 slow removal of the New Red Sandstone 

 in which it was embeded. 



