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REV.

 R. 
 BARON 
 ON 
 THE 
 GEOLOGY 
 OE 
 MADAGASCAR. 
 305 
 

18.

 Notes 
 on 
 the 
 Geology 
 of 
 Madagascar. 
 By 
 the 
 Rev. 
 E. 
 Baron, 
 

F.L.S.,

 F.G.S. 
 With 
 an 
 Appendix 
 on 
 the 
 Fossils, 
 by 
 R. 
 B. 
 

Newton,

 Esq., 
 F.G.S. 
 (Read 
 March 
 6, 
 1889.) 
 

.Communicated

 by 
 the 
 Director-General 
 of 
 the 
 Geological 
 Survey.. 
 

.Plates

 XIII. 
 & 
 XIV.. 
 

General

 Description. 
 

Madagascar

 is 
 as 
 yet 
 almost 
 a 
 terra 
 incognita 
 to 
 the 
 geologist, 
 

nothing,

 so 
 far 
 as 
 I 
 am 
 aware, 
 but 
 notices 
 of 
 the 
 most 
 fragmentary 
 

kind

 ever 
 having 
 appeared 
 in 
 regard 
 to 
 its 
 geological 
 features 
 * 
 ; 
 

and,

 indeed, 
 until 
 the 
 country 
 is 
 surveyed 
 by 
 competent 
 men, 
 we 
 

must

 be 
 content 
 with 
 descriptions 
 of 
 the 
 most 
 general 
 character. 
 

In

 the 
 absence 
 of 
 something 
 more 
 complete, 
 I 
 present 
 the 
 following; 
 

notes,

 drawn 
 up 
 from 
 personal 
 observation, 
 to 
 which 
 1 
 have 
 added 
 

here

 and 
 there 
 a 
 few 
 remarks 
 taken 
 from 
 other 
 sources, 
 as 
 a 
 slight 
 

contribution

 to 
 our 
 knowledge 
 of 
 the 
 geology 
 of 
 this 
 great 
 island. 
 

The

 central 
 portion 
 of 
 Madagascar 
 is 
 generally 
 regarded 
 as 
 consist- 
 

ing

 chiefly 
 of 
 granite. 
 Mr. 
 Wallace, 
 for 
 instance, 
 in 
 his 
 ' 
 Island 
 Life 
 ' 
 

(p.

 384), 
 says 
 of 
 it 
 : 
 "A 
 lofty 
 granitic 
 plateau, 
 from 
 80 
 to 
 160 
 miles 
 

wide,

 and 
 from 
 3000 
 to 
 5000 
 feet 
 high, 
 occupies 
 its 
 central 
 portion, 
 

on

 which 
 rise 
 peaks 
 and 
 domes 
 of 
 basalt 
 and 
 granite 
 to 
 a 
 height 
 of 
 

nearly

 9000 
 feet 
 ; 
 " 
 and 
 in 
 the 
 same 
 book 
 there 
 is 
 a 
 physical 
 sketch- 
 

map

 in 
 which 
 the 
 whole 
 of 
 the 
 interior 
 of 
 the 
 island, 
 from 
 about 
 14° 
 to 
 

23°

 S. 
 lat., 
 is 
 represented 
 as 
 an 
 " 
 elevated 
 granitic 
 region." 
 Now 
 if 
 

we

 use 
 the 
 terms 
 " 
 granite 
 " 
 and 
 " 
 granitic 
 " 
 in 
 a 
 wide 
 and 
 popular 
 

sense,

 and 
 include 
 in 
 them 
 the 
 various 
 members 
 of 
 the 
 crystalline 
 

series

 of 
 rocks, 
 the 
 description 
 may 
 be 
 regarded 
 as 
 correct 
 ; 
 for 
 by 
 

far

 the 
 greater 
 part 
 of 
 the 
 eastern 
 half 
 of 
 Madagascar 
 consists 
 of 
 

gneiss

 and 
 other 
 crystalline 
 rocks, 
 though 
 gneiss 
 very 
 largely 
 pre- 
 

dominates.

 Granite 
 occurs 
 frequently 
 in 
 the 
 form 
 of 
 bosses 
 and, 
 in 
 

some

 places, 
 apparently 
 intercalated 
 with 
 the 
 crystalline 
 schists 
 ; 
 

diorite

 is 
 also 
 frequently 
 met 
 with, 
 but 
 gneiss 
 is 
 certainly 
 the 
 pre- 
 

vailing

 rock. 
 The 
 area 
 occupied 
 by 
 these 
 ciystalline 
 rocks, 
 though 
 

not

 precisely 
 known, 
 reaches 
 on 
 the 
 east 
 as 
 far 
 as 
 the 
 coast 
 : 
 on 
 the 
 

west

 it 
 extends, 
 in 
 some 
 places 
 at 
 least, 
 as 
 far 
 as 
 46° 
 E. 
 longitude 
 f 
 ; 
 

and

 it 
 runs 
 in 
 a 
 northerly 
 and 
 southerly 
 direction 
 from 
 about 
 13° 
 50' 
 

to

 24° 
 S. 
 latitude. 
 In 
 other 
 words, 
 the 
 region 
 occupied 
 by 
 these 
 crys- 
 

talline

 (chiefly 
 metamorphic) 
 rocks 
 has 
 a 
 length 
 of 
 about 
 730 
 miles, 
 

and

 an 
 average 
 breadth 
 of 
 probably 
 not 
 less 
 than 
 150, 
 being 
 a 
 total 
 

area

 of 
 over 
 100,000 
 square 
 miles. 
 Indeed 
 it 
 is 
 not 
 at 
 all 
 improbable 
 

that

 the 
 area 
 may 
 cover 
 as 
 much 
 as 
 130,000 
 square 
 miles. 
 Fully 
 

a

 half 
 of 
 the 
 island, 
 therefore, 
 and 
 that 
 the 
 eastern 
 half, 
 consists 
 of 
 

 The 
 MS. 
 of 
 the 
 present 
 paper 
 was 
 prepared 
 long 
 before 
 Cortese's 
 contribu- 
 

tion

 in 
 the 
 Bollettino 
 del 
 R. 
 Com. 
 Geol. 
 1888, 
 Nos. 
 3 
 & 
 4, 
 was 
 published, 
 

t

 Its 
 most 
 westerly 
 limit 
 is 
 probably 
 about 
 45° 
 50'.